What Has Four Wheels and Flies?

Two jobs for one word

Heard as a verb, "flies" describes something that leaves the ground, so listeners think of planes, and then wonder how a plane can have four wheels. The answer uses "flies" as a plural noun, the insects. A garbage truck has flies because garbage attracts them: house flies lay their eggs in rotting food waste, so uncovered cans and dumpsters draw them in numbers.

The sentence has no extra clue to help. The same words make a sensible question and a sensible answer, which is what gives the riddle its pop.

Why collection day

Emptying cans often and keeping the lids tight are the usual ways to keep flies down. A truck that comes on a schedule is part of that routine, so the riddle's picture of a truck with flies is a fair one.

The wheel count

Garbage trucks come in different sizes, and the number of wheels depends on the model. Treat "four wheels" as the riddle's round figure, not as a measurement. It only has to suggest a vehicle.

Other names for the answer

Americans say garbage truck or trash truck. In British English the same vehicle is a bin lorry or a dustcart. A listener who offers one of these names has given the right answer.