Explanation: After you finish eating you could say, “I am full” or you might say, “I’m stuffed.” Both expressions mean the same thing: you have eaten enough and you do not need to eat any more.
If you were to open a teddy bear you would find “stuffing” inside. Stuffing is the material that makes the bear soft and cuddly. Teddy bears are also known as “stuffed animals,” that is, toy animals that are soft and are full of stuffing.
This joke plays on the double meaning of the word “stuffed.” Of course teddy bears are stuffed! But they never eat anything.