Speaking of costumed elephant :

When filming the movie Quest for Fire (la Guerre du Feu) director Jean-jacques Annaud wanted real elephants to play the roles of mammoths. He asked the Zavatta Circus to dress up two elephants with the fake mammoth fursuits done by his props department.

But unfortunately, they dressed each elephant in a separate corner of the circus tent, separated by curtains.

When they lifted the curtains to walk the elephants outside for the photo department to snap reference shots, they ended up with two rampaging elephants running away from each other, detroying trailers and tents in their scare.

It turned out they completely forgot that an elephant could be scared to death by an encounter with an unknown animal of his own size, especially if it looked like "a montruous hairy elephant with giant tusks".

Imagine how you would react to an encouter with a gorilla in your bedroom !