The late night host had his co-stars practicing how to meow, how to walk through a door as a cat and how to be mean towards a dog.
A giant ball of yarn, bowl of milk and a litter box was also present. Derulo was forced to use the litter box in front of everyone when he needed to use the bathroom while Swift had to drink from the bowl Wilson had spiked with alcohol.
"I was just recently named artist of the decade, but after people see me lap up milk from that giant saucer, I'm pretty sure that they will take that away," Swift said.
Hudson was named Best In Show and was presented a trophy by Andrew Lloyd Webber who created the original Cats Broadway musical the film is based on.
"I won an Oscar for Dream Girls and now I've won Best In Show for being a cat. I mean, where do I go from here?" Hudson said.
Cats opens in theaters Friday.