The 31-year-old – who replaced Carol Vorderman to present the Channel 4 quiz show – appeared a little red-faced as she looked away from the screen nervously while spelling out the word “squirter”.
Unsurprisingly, viewers immediately took to Twitter to laugh about the whole thing.
One person said: “Rachel Riley’s face on Countdown when Dictionary Corner said they could’ve had Squirter for 8 points.”
“Your face @RachelRileyRR ‘SQUIRTER for 8’ #countdown,” a second joked, alongside numerous laughing emojis.
A third wrote: “@RachelRileyRR face when squirter was mentioned on @C4Countdown today was so funny.”
While a further social networker posted: “Found this quite amusing when watching #countdown today. #MidweekMadness @RachelRileyRR.”
This certainly isn’t the first time that Rachel has suffered an incident like this on the show, with her previously spelling out the likes of “bulge,” “bumhole” and “vibrator”.
It comes after she previously gave Countdown viewers more than they bargained for after she suffered one almighty wardrobe mishap in a throwback episode.
Rachel donned a tight-fitting pink number and marked the occasion by going braless.
In turn, eagle-eyed viewers noticed that the daytime TV beauty was sharing a hint of nipple and all before the watershed.
Countdown continues tomorrow at 2.10pm on Channel 4.