WARNING: The following contains spoilers for One Piece Chapter #1030, "Echoing The Impermanence of All Things" by Eiichiro Oda, Stephen Paul, and Vanessa Satone, available in English via Manga Plus and Viz Media.
What would you do if a pair of disembodied, bloody legs came running toward you, literally talking out of their butt? Most would probably run away in terror, but thankfully in One Piece, Usopp realizes the legs in question belong to a friend. Kin'emon, who was thought to be killed by the devious Kaido, is in fact alive. Unfortunately, he's still pinned to the floor where he fell -- well, half of him is. The other half is with Usopp, giving him directions on where to find Kin'emon and Kikunojo, who are both barely hanging on. But how is this possible?
Even Kin'emon isn't exactly sure how he survived, but he speculates that it's thanks to Trafalgar Law. Back on Punk Hazard, he and Trafalgar got into a tiff and the surgeon separated his body, hiding the different parts all over the island. Kin'emon believes that when he was eventually reassembled, it wasn't complete and his torso was never properly reattached to his waist. This is what ultimately saved him when Kaido impaled him with his own sword later on.
Despite being played for laughs, One Piece's imagery here is rather dark. What about Kin'emon's internal organs? Are they just flopping about while the legs run, or are they laying on the floor back with his torso? He's been in other fights since being reassembled, so why didn't he separate before if he wasn't properly attached to his legs? How is Kin'emon controlling the legs and (literally) talking through his rear? Are the legs sentient and able to run around on their own? There are so many questions about how this is actually happening.
It's possible that Kin'emon is able to concentrate and control the legs. Like he tried to stand up once he realized he survived, but only half of him moved. He doesn't really move the upper portion of his body when we see it, so it's possible all of his energy is going into controlling the legs. But that leads to another question: how is he able to feel sensation in the legs if his spine has been severed? Nami signaled that they were there by tracing the Crescent Moon of the Rebellion on his legs, but how was Kin'emon's torso able to feel it if his spine is split in two?
Of course Eiichiro Oda can't show all the gruesome details of how this is actually possible, given that this is published in a serialization made for teenagers and kids. But even without being detailed, it's still not something you see too often in media with such a young demographic. Yes, One Piece can be violent since it is a battle manga for the most part, and violence comes with the territory. People die all the time in this story. But the idea of someone's bloody legs running around the battlefield looking for help is kind of horrifying.