You listen more to what this quack says than what the doctor says.

The cow goes "moo," the rooster goes "cock-a-doodle-doo," the pig goes "oink, oink," the duck goes "quack, quack" and the cat goes "meow."

In "A Journal of the Plague Year," a 1772 fictionalized account of London's Great Plague of 1665, Daniel Defoe notes that people were quick to turn to quacks and peddlers offering "Sovereign cordials against the corruption of the air."

A duck quacks.

Ducks quack.

He must be a quack doctor.

Quack, quack!" the duck said.

The cow moos, the rooster crows, the pig oinks, the duck quacks, and the cat meows.

The ducks quacked.

The duck quacks.