A good definition of a pun is, “A joke or type of wordplay in which similar senses or sounds of two words or phrases, or different senses of the same word, are deliberately confused”.
In the picture above, the toys are “stuffed toys” meaning they were made by inserting stuff (materials) inside to give them shape and form. At the same time, “stuffed” means eating in excess. Thence, the pun. Arrivederci!