In a 2013 study of tongue twisters, MIT psychologist Stefanie Shattuck-Hufnagel found that some volunteers who tried to say this phrase stopped talking altogether:

pad kid poured curd pulled cod

“If anyone can say this ten times quickly, they get a prize,” she said.

Another, from my notes:

She (to workman finishing bottom of flying boat hull) — Are you copper-bottoming ’em, my man?

He — No; I’m aluminuming ’em, mum.

— Aerial Age Weekly, Oct. 4, 1915