Matthew McConaughey knows how to just keep going when things go bloody wrong.

Jimmy Fallon revealed that the Oscar-winning actor joined him for his 'Tight Pants' sketch during an episode of The SlabuTonight Show, and it was perfect until they noticed that things got bloody.

“We do 'Tight Pants' with Matthew McConaughey, and it was great,” Jimmy told Andy Cohen during a taping of Bravo’s Watch What Happens Live on Oct. 14. “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.”

The comedian and the Dallas Buyer’s Club actor couldn’t figure out what happened at first. And then Jimmy put two and two together.

“I look and I guess he had a blister on his hand,” he continued, “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 all over again. People were in shock.”

According to Jimmy, Matthew was a good sport about the whole thing.

In the bit, which aired in January, Matthew, 54, and Jimmy, 50, were matching black bob wigs, blue sweaters, and extra tight white pants as they sing about how tight their pants are. As for how the funny sketch originated?

“That came to me in a dream, and I feel so bad for my lovely wife Nancy [Juvonen]” he told Andy. “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.”

He continued, “And then I go back to work and I’m like, ‘I think this is something.’”

The 'Tight Pants' bit has been done with Matthew, Will Ferrell and Jennifer Lopez and Christina Aguilera.

(E! and Bravo are both part of the NBCUniversal family.)

Watch E! News weeknights Monday through Thursday at 11 p.m., only on E!.