"He has clearly reacted to a poorly performed Imperius Curse. It's addled his brains, but he could still be dangerous."
"He's only quacking!"
-- conversation between Cornelius Fudge and the Muggle Prime Minister (HBP1)
Herbert Chorley was a Junior Minister to the British (Muggle) Prime Minister
Chorley had a bad reaction to a Death Eater's Imperius Curse and began impersonating a duck. The Prime Minister had thought his Junior Minister might have a problem with drink.
Chorley was subsequently hospitalized at St. Mungo's, where he attempted to strangle several Healers (HBP1).