In the new Western 'True Grit,' Matt Damon's character gets injured while being dragged behind a horse, and nearly bites off his tongue. So, Matt needed to find a way to imitate the sound of a speech impediment. "So I thought, well, what if I wrapped -- like -- a pony tail around my tongue," he said.

Which is a bit of a mental leap, but okay. And for the record, by "pony tail," he's referring to a hair-tie, or a "scrunchie" -- not anything to do with actual horses. On the 'Late Show' (weeknights, 11:35PM ET on CBS), Damon invited David Letterman to join him in the unique practice of talking with a hair-tie on your tongue. "I brought one for you," he said. "Did you bring two? Or just the one?" the host asked.

"Just the one ... it's got lint on it," Matt replied, reaching into his pocket. (That's not very sanitary, Matt!)

Luckily, after some quick scrambling by Dave's "people," a second hair-tie was located. (Which would be nice, by the way, to have "people" to bring you things like that.) The pair then tried the hair-ties on ... "ALRIGHTHT," Dave said. "WELLTH, SO FAR, IT'SH NOT THAT BAD."

"IT'STH EFFECTIVE," Letterman added, "BUT I THOUGHTTH IT WOULD BE PAINFUL."