Rachel Riley had to spell out a rude word on Countdown. She couldn’t keep a straight face.

No matter what age you are, rude words are always, always funny.

But if someone is forced to spell them out on television? Even funnier, as Rachel Riley found out.

Pasha Kovalev joined his girlfriend Riley on Countdown, the Channel 4 quiz show she co-hosts.

Kovalev appeared on the show as a lexicographer alongside Susie Dent. He casually suggested to Riley that the words on the board, MEPHALSUL, could be rearranged to spell out the word "phallus," which is basically a fancy word for penis.

"Sorry, I was just a bit stunned for a second," said host Nick Hewer as Riley stood at the board, demonstrating that the word jumble could, in fact, spell this delightful word.

Here's the video, for your viewing pleasure:

More: Using more swear words is actually a sign of a larger vocabulary

More: 14 long-lost English swear words ranked in order of offensiveness