"And he turns around there's blood all over his white pants, handprints and blood," Fallon recalled of McConaughey's Tight Pants sketch on The Tonight Show.
Matthew McConaughey sported some very tight ... and very bloody ... pants on The Tonight Show with Jimmy Fallon.
While sitting down with Andy Cohen on Watch What Happens Live Sunday night, Jimmy Fallon revealed the gross-out reason the Oscar-winner had to do a second take of Fallon's iconic, "Tight Pants" segment.
While Fallon thought everything went perfectly their first run, the host then noticed bloodied hand prints all over McConaughey's white pants.
“We do 'Tight Pants' with Matthew McConaughey, and it was great," Fallon told Cohen after the face of Bravo finished telling him how much he loves the "Tight Pants" sketch.
"And at the end we do the whole bit and we get into a fake argument. And he turns around there's blood all over his white pants, handprints and blood," Fallon continued.
After looking at McConaughey's hand, Fallon discovered the actor had popped a blister after slapping his own rear-end too hard.
"I look and I guess he had a blister on his hand," said Fallon, adding how athletic the actor is, how he's a "carpenter" and how he "does stuff."
"He slapped his butt so hard that he blew open a blister on his hand, and we had to find tight white pants and do the sketch again. People were in shock," Fallon continued.
Luckily, production was able to locate another pair of white pants that fit the 54-year-old star, so the pair could redo the sketch that aired back in January.
In the hilarious bit that big names such as Will Ferrell, Jennifer Lopez, Christina Aguilera and more have appeared in, the stars wear matching bob wigs, blue sweaters, and extra tight white pants as they sing about how tight their pants are.
"That came to me in a dream, and I feel so bad for my lovely wife Nancy [Juvonen]," Fallon told Cohen.
"But we're in bed one night and I just wake up and I just record ideas. So I go, 'Everybody's talking about my tight pants, about my tight pants I got my tight pants on.' And then I go back to sleep."
And the rest is history.