Eagle-eyed viewers spotted what appeared to be a live mouse on This Morning on Monday.
Those watching were left in shock as a dark shape appeared to scuttle past Holly Willoughby's shoulder as she was presenting details of a phone-in.
Viewer Chloe Robinson was quick to notice the shocking sight, sharing a video of the blink-and-you'll-miss-it moment.
Nicole Cunningham added a disgusted face as she asked whether she'd just seen a mouse.
But Holly, who has just returned to the show after a family break to Portugal, seemed oblivious to the rodent-shaped creature behind her.
Other viewers seemed to have worked out an alternative explanation for the appearance of the "mouse" after Phillip Schofield denied it was a critter - it was the head of someone walking past the studio's window.
ITV have been contacted for comment on what it really was.
But the rodent - imaginary or not - has become so popular it's even sparked a fan club of those desperate for their own vermin infestation.