It was this creepy octopus-like thing with tentacles that had poisonous stingers on them. And the men on this planet...Arboria, I think....had to prove their manhood by sticking their arm down in one of the openings to the center of the tree trunk(there were a bunch of openings). And this thing is like sitting in there...waiting. And if it stung you, you would eventually go mad, so usually some guy would take your head off to spare you the long painful insane death.
How pleasant.