Sittin' Muscle is the 8th episode in Season 1, and the 15th episode of the series overall. In this episode, Flapjack and K'nuckles journey to the Bottom of the World in search of K'nuckles's long lost Sittin' Muscle.
Flapjack and K'nuckles noticed an old ship sail in to port. K'nuckles immediately recognized her, the S.S. Disaster, and states she left at least eighteen years ago. Once the owner and captain of the ship, Captain Ridiculous, steps out, a crowd gathers around him, and he tells them he's back from The Bottom of the World (Antarctica) and requests them all to go to Storytime Tavern where he can tell them what happened in his travels. Flapjack and K'nuckles head off to hear the story, but are forbidden to enter Storytime Tavern, so they eavesdrop through an open window. Before Captain Ridiculous began to tell his story, he pulls out a flip-chart. Using the Flip-chart, he tells his tale with cheap, hand-drawn illustrations. His story basically went like this: They traveled to Antarctica, surveyed and mapped it, met a little old man, and became the first creatures to scale a previously insurmountable mountain.
However, while showing a cheap picture of the mountain, something else on Captain Ridiculous' drawing catches K'nuckles' eye. He instantly spots a sloppy oval drawn close to the summit. While in shock, mouth agape, Flapjack asks K'nuckles why he looked so surprised. It was then that K'nuckles revealed an embarrassing part of his past. He tells that many years ago, most of his rear end was amputated from his body, thus most of his backside is now wooden. In shock, Flapjack declares: "You have a wooden bottom?!" Embarrassed, K'nuckles insists that it is his "'sittin' muscle", which sounds more dignified to him. After arming themselves with this knowledge, Flapjack and K'nuckles sail toward Antarctica on Bubbie to recover the Captain's posterior. While on the way, Flapjack curiously asks how K'nuckles lost much of his gluteus maximus, though in respect, corrects it to "sittin' muscle".
Not wanting Flapjack to know the truth, K'nuckles conjures up a tall tale. He claims that he was captaining a boat near Antarctica, alone with no crew, when suddenly, a demonic, tentacled, swimming rabbit thing made of ice rises from the deep, and attacks! K'nuckles fights back and manages to free himself from its grasp, but he lost an important part of his body in the process. The beast then sneezed K'Nuckles's butt clean off, which, as K'nuckles claimed, was the reason his "sittin' muscle" ended up on the mountain. Naturally, Flapjack believed it, and praised K'nuckles as a great adventurer, then commended him on his bravery under pressure.
Moments after K'nuckles finished his story, Bubbie collided with Antarctica's Ice shelf, and the force cracked it into thousands of small icebergs. Bubbie was unable to travel any further, and the Mountain was far away. This forced Flapjack and K'nuckles to walk on top of the ice bergs, and in his overbearing excitement, K'nuckles carelessly accelerated to high speeds on the slippery ice, and was unable to obtain enough momentum to stop when he reached Antarctica's shore. Unfortunately for him, he continued to slide until he collided with a massive continental glacier! There was a good side to the collision, however, as the force of the impact shattered around fourteen fifteenths of the glacier, all but the very "bottom", which could easily be walked over. Beyond the shattered remains of frozen precipitation, a mountain range could be seen. Among the summits was the mountain where K'nuckles' "sittin' muscle" lie preserved, untouched for years. Alas, the coveted caboose was on the highest mountain on the continent. If you recall, it was stated earlier that the impact only shattered the majority of the glacier. This gave the impression both to the adventurers and the viewers that the mountains were dead ahead. Unfortunately, the last piece of the continental glacier disintegrated, revealing a long, winding trail to the range. They had a long way to go.
After many hours of walking, they came across a research station. The little old man that Captain Ridiculous mentioned at the start of the show walked out. He incorrectly recognized K'nuckles and Flapjack, thinking they were part of Ridiculous' crew. K'nuckles quickly corrected that statement, saying they were "just friends". Delighted to meet a supposed acquaintance of the Captain, the old man declared "Any friend of Captain Ridiculous is a friend of mine!" Flapjack excitedly told the senior citizen that they were going to scale the insurmountable Mountain to reclaim K'nuckles' bottom, which he once again immediately corrected to "sittin' muscle". The old man, being a veteran arctic survivor (he has lived at the Bottom of the World for many years), immediately told our adventurers what to do next. He was going to give them free insulated clothing to keep them from contracting hypothermia. While the old man went to fetch the parkas, K'nuckles, in utter ignorance and greed, told Flapjack the (wrong) truth. "That guy's a con man!" K'nuckles proclaimed. He continued, and gestured to the sun, which was at its highest point of the day: "Look how close to the sun that mountain is! It must be blazing up there! Why would we need to BUY warm coats with all that FREE heat?"
Flapjack, of course, unconditionally trusted K'nuckles, and ran off with him for the mountain screaming "ADVENTURE"! The old man came back with the coats and said: "Hello again friends! I've got these warm clothes for you. You can keep them as long as you like. Why, you don't even have to give them back!" Unfortunately, K'nuckles and Flapjack were long-gone, completely oblivious to the fact that they were going to freeze, AND that the parkas were free. K'nuckles was so oblivious, in fact, that he threw off his robe and undershirt, stashed them away, and continued on wearing nothing but his trademark hat. K'nuckles got so cold, he couldn't move, forcing Flapjack to tie him to a rope like a mountain climber, and drag his motionless heap up the mountain for him. At the summit, K'nuckles finally had the sense to put his garments back on, but the damage was done. He was shivering, stuttering, and showing all the signs of hypothermia. Suddenly, he saw it! Running toward a clear sheet of ice, he proclaimed: "There it is! It's your sittin' muscle! Notice how i didn'td say bottom?" Unfortunately, K'Niuckle's "sittin' muscle" was encased in.
Flapjack, who was also freezing by this time, suddenly recalled that he still had two sticks to make fire with! Unfortunately, he didn't have any kindling, so he was forced to use the wooden portion of K'nuckles' remaining backside. He started rubbing the sticks to together, on top of the booty kindling, and the friction successfully stared a fire! The fire burnt the wooden bottom to ashes, failing to warm them. K'nuckles decided to tell Flapjack the real story of his behind due to their likelihood of dying.
K'nuckles started out saying that he wasn't actually the captain of a ship, that there was no rabbit tentacle monster, and he wasn't alone. In fact, he was a cabin boy on the S.S. Disaster! K'nuckles went on. Down below deck, after a successful day of finding Antarctica (this was long before the expedition mentioned at the start of the episode), the buff sailors and K'nuckles as a child were sitting and having idle, yet boasting chit-chat. The young K'nuckles had his signature prosthetic hands and feet by this time, but his entire backside was still attached to his body. That wasn't going to be true much longer. It started with one sailor with incredibly muscular arms stating that "my incredibly awesome arms are sore and tired from lifting and working out all day." That received complements from his fellow shipmates. A second sailor joined in, saying "my fists (which by the way had 10 fingers on each fis3t) are in pain because I broke a guy's nose with it!". The man with the damaged nose chimed in, stating that his "nose was sore, from hitting someone's fists!" The sailors also commended him for being so tough. Little K'nuckles, thinking he was tough as well, stated in absolute elation: "My bottom is sore from sitting on it!" This comment was taken to offense to the sailors because their reasons were far more valid,and the fact that knuckles called it a bottom, not a sittin' muscle (thus starting the botom sittin' muscle thing). In an act of revenge, they knocked the little guy out, amputated his backside, and after he regained consciousness, they started to tease poor little K'nuckles, who now limped unstably because he lost every part of his backside that didn't serve... "digestive" purposes. The sailors, who were much taller than K'nuckles, proceeded to play "Monkey in the Middle" using the junk from little K'nuckles trunk. The sailor with the huge arms, as a final act of cruelty, threw K'nuckles' backside upward, toward the wall, but it crashed through the boat's hull and flew into the mountain, were it remained preserved in ice to that day.
K'nuckles was very embarrassed and depressed, but Flapjack didn't laugh at him. Instead, he gave K'nuckles a great hug, which he quickly rejected, using the last of his strength to push him away, then said "Adventurers don't give hugs...", and passed out. Flapjack ignored that, and gave K'nuckles an even bigger hug. The warmth from Flapjack's body revived K'nuckles, who was about to detest his hug once more, when he took a glance at his frozen "sittin' muscle", and noticed that it was thawing. In fact, the more Flapjack hugged K'nuckles, the more the ice melted from his body heat. K'nuckles, suddenly excited again, told Flapjack to "Keep hugging!" and to "Hug harder!" Well, Flapjack did, the angelic background choir sang "Power huuuuggggg!" holding that note for a few seconds, until the ice completely melted, and K'nuckles rear was thawed. An elated K'nuckles, now revived due to Flapjack's body heat, ran over and reattached his hind quarters. He reluctantly thanked Flapjack, and commenced walking around, Flapjack in tow. K'nuckles didn't have a clue on how to get down, but he accidentally slipped on some ice, and he and Flapjack started rolling down the hill in an old-fashioned cartoon snowball, and landed, rear-end first, right in front of the old man, who laughed and said "I told you you needed those coats!"
The screen faded to black, and the Storytime Tavern is shown once more. Captain Ridiculous is shown again, this time with K'nuckles and Flapjack encased in solid ice. He said "A few days ago, I found this while sailing to The Bottom of the World. It seems to be two primitives encased in ice. One is an idiot, while the other seems to have evolved without a backside." Flapjack managed to move his mouth and said "sittin' muscle"! All K'nuckles could do was moan and roll his eyes.