Riley revealed during an interview with The Mirror that her co-host Nick Hewer is often oblivious if an answer crops up that has to be edited out for compliance reasons.
> Nick Hewer interview: 'The country depends on Countdown'
"Usually Nick doesn't realise. Sometimes he hasn't noticed, as he's a little bit eccentric," she told the paper.
"They just have to cut away from me because I'm cracking up, while Nick is oblivious."
Explaining that "you can't have blatant filth up there [on the board]", Riley added that the decision as to whether a word will be left in the programme or not often hinges on her reaction.
Riley said: "We've had some bad stuff come out. It's not too often, but if I'm just standing there next to the word 'f**k' then that can't go out - and that has happened to me. On other occasions, if I giggle as the letters come up, then it's definitely out.
"There are rules for it, it just depends on the actual word. I remember when I was quite new a bloke came up with an eight-letter word, 's**tface'. Obviously that can't go out but it is a word, so they had to quietly alter it and give him a new word in its place and edit that one in instead.
"Then, there are some words which are quite innocent but can have a different meaning these days."
Watch a Countdown contestant winning points on the show with the word "w**ker" below: