Here’s a faintly seasonal mix-up with an accompanying adorable picture.

Foul

• offensive, obscene or vulgar; unpleasant
• foul smelling or dirty; full of dirt or offensive matter
• evil, wicked or immoral
• bad tempered, cross or irritable
• unfair or dishonorable; against the rules of a sport
• to make dirty or polluted; to spoil or damage
• to come into conflict with (‘fall foul of’)

Fowl

• a domesticated bird such as a chicken
• a bird raised or kept for food, or hunted as game
• the meat of fowl
• a bird; a collective term for birds

Ducklings are fowl and not foul. (Although, like all baby things, they are full of offensive matter that will go everywhere. And it stains. So I think that illustrates foul/fowl is a matter of perspective.)