Choose which joke you like more:
1) There was a rabbit in this yard, and whether ironic or not, the passers-by were alerted to the pet by a "Beware Of Bunny" sign. Then a huge dog ate the bunny. Then Garfield came by, wondered where the rabbit was, and was horrified when the dog revealed his massacre by loudly belching.
2) The purple-gray Madame Mim-esque animal sitting in the yard is supposed to be a grotesquely outsized man-weight rabbit. Garfield is aghast that such a monstrosity could be called "bunny".
3) Some unfathomable conflation of #1 & #2.