Six words create the world's most difficult tongue twister.

MIT researchers unveiled a study this week at the 166th meeting of the Acoustical Society of America wherein they looked to find more information on how the human brain works by utilizing two different types of tongue twisters.

One phrase, in particular, was impossible for study volunteers to say ten times fast. That phrase?

Pad kid poured curd pulled cod.

Yes, yes--you can say it slowly. We're all very impressed. Now, as your mother would say, try challenging yourself.