If you think dogs can't count, try putting three dog biscuits in your pocket and then giving Fido only two of them.

The joke hinges on the gap between formal “counting” and practical awareness. Even if a dog cannot perform arithmetic, it can notice when an expected reward is missing—through smell, routine, or a rudimentary sense of quantity. Pastoret uses that everyday insight to satirize human condescension toward animal intelligence: the dog’s reaction becomes evidence that our definitions of intelligence are too narrow. The line also works as a miniature lesson in empiricism—don’t rely on assumptions; test them—while remaining firmly comic because the “test” is mischievous and the dog (Fido) is a stock character.