Ahead of a segment with vet Scott Miller, the 60-year-old welcomed the animal expert to the show with his wife Ruth Langsford.
Plugging the segment, which focused on debunking the myths surrounding black cats, Eamonn said: "Are you superstitious about things like a black cat crossing your path?"
Suddenly, Scott appeared on the screen with a black kitten cradled in his arms, as Eamonn exclaimed: "Nice p***y!"
Ruth tried her best to suppress a giggle, while Scott was a little less successful, as his laughter erupted during the interview.
Trying to control himself, he replied: "Thank you Eamonn, yes."
Meanwhile, over on Twitter, viewers were floored by the expression, with many associating the term "p***y" with the slang word for female genitalia – though it also refers to cats.
One wrote: "Nearly spat my tea out when @EamonnHolmes said ‘nice p***y'."
And a second wrote: "Nice P***y?!? @EamonnHolmes on #ThisMorning."
"Why would @EamonnHolmes just say ‘Nice P***y' like that @thismorning #jokers #loveit," added a third.
Later in the episode, TV vet Scott visited an animal sanctuary in Shropshire to investigate the superstition surrounding black cats.
Speaking with the volunteers in the shelter, Scott learned black kittens were often the last to be adopted by owners, as viewers still associate them with the spooky superstition.
One of the centre's workers explained that black cats "don’t photograph very well," before adding: "So when people are looking online, they often go for the prettier colours and these are often left on the shelf."
Showing off a variety of adorable black cats available for adoption, Scott urged viewers to give the furballs a chance.
Praising the kittens on display back in the ITV studios, Eamonn conceded: "Absolutely beautiful beasts it has to be said."
This Morning airs on weekdays at 10am on ITV.