This comic is much more complex than it appears at first glance. We see that Marmaduke considers his owners to be little more than glorified waitstaff. We also see that he is a stingy tipper… he left maybe a buck fifty. A dog the size of Marmaduke likely eats $30 worth of dog food in a single sitting. What a bad tipper!
But then again, maybe it’s not a tip. Maybe it’s hush money. Marm is telling his owners to go ahead and forget that they saw a human baby in his dogdish. The family smiles on the outside but they are horrified on the inside. The exclamation of “He left us a tip” is for the FBI, which has been monitoring the Marmaduke household for years now. In this case, the amount of money left might be even more insulting but it’s obvious that it’s a symbolic gesture, like a single rose or a horse’s head left in the bedsheets.
In other news, Marmaduke’s legs appear to be turning into snakes.
Final verdict: Marmaduke either eats babies or is a lousy tipper