If you have taken Latin, you learn that their were no trap doors for the animals to jump out of. The Colosseum floor had wooden planks that covered the cages where the animals were held. It also served as the floor that the gladiators fought on. The planks were covered in sand. That's where they get the word ARENA. "are" means sand. They had sand to soak up the blood. Basically what I'm trying to say is that there were no trap doors in the Colosseum.