The hat that magicians wear usually have a secret compartment that will be able to fit the rabbit easily and comfortably. What the magician should do is to make it appear like the hat is just lightweight even though the rabbit is already inside the hat. The compartment will open at the right time and the magician will successfully pull the rabbit out of the hat.
There are some aspiring magicians who are still practicing this tip. Instead of using a real rabbit, they would use a stuffed toy instead. This will help make sure that no rabbits are harmed during practice. There are other magicians who have used other animals provided that the animals are small enough to fit the compartment.