Body
This radical is almost the same as the kanji, but it drops the "some" from somebody, making this just a body. Like the physical body you're trapped in right now.
Just in case you don't remember the kanji meaning, here's the mnemonic again: Sure, it’s yourself who’s tumbling down the slide… at least that’s how it feels to you. Who are you? What are you? All you know is you’re somebody, but you don’t know who that somebody is.