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I don't think that's it. I can't find the scene I'm thinking of in particular. At the time I thought it was pretty strange, but Fantastic seems like it's probably even stranger. Thanks though.
EDIT: I'm not even sure if it was really giant crabs so much as I recall giant pinsirs, which were used to cut the loin-cloth brigade in half. It might be Fantastic Planet if theres a scene like that in there, but there's no youtube videos and nothing on the Fantastic Planet page about it. I'm positive I didn't see any blue aliens though. I believe there was someone narrarting it, but I don't know if that'll help.
Edited by TheGorramBatmanThis reminds me of La Planète Sauvage
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Not sure anyone can help with this one, and I'm also not sure if it's really anime or western animation, but i recall some years ago seeing a scene in an animated movie that was being played on starz (Could have been HBO, cinemax, or showtime as well I guess, but I'm 99.9% positive it was starz). involving these giant crab things (I think they were black, but I could be wrong). There were these scantily clad humans rushing them with spears, and if I'm not mistaken a lot of people got cut in half by the crabs' far superior claws. I think it was from the late 80's early 90's, but I don't know for sure. I didn't think to check for the name, and I've been dwelling on it for years now. I've kept it at the back of my mind for the most part, but every now and then it pops back up and drives me nuts.
EDIT: I seem to recall the crabs coming down the side of a mountain.
EDIT: The humans might have all been bald too. I can't remember for sure but I have a feeling they were. Also there's a possibility they were all men. There were a lot of humans; they were like an army. The scene looked as if they were fighting a war. And the thing I remember best is people getting cut in half by the crab-things. I think their spears just broke when they hit the crabs. That is if they even connected. Can't remember.
Edited by TheGorramBatman