yoshi was giving them the silent treatment and they didn't know why, but they could tell something was eating at him.
A prank is something you can laugh about later. The best result of this is he wakes up with a dead eel in his ass. Not exactly something to be laughing about later.
Asian women stick these things up their vagina all the time and I've never seen one of them die...
If that dude was conscious for it, I can't imagine a much worse way to die.