There has been many a blooper that has emerged in recent years from Friends that totally went unnoticed by fans back in the days when we couldn't just pause and rewind what we were watching. From stand-ins appearing in the shot when they shouldn't to one too many Phoebe's, there's plenty that we missed.
An eagle-eyed fan recently spotted a blooper by Joey from an episode in the sixth season of the sitcom.
In The One Where Ross Dates a Student, Joey (Matt LeBlanc) can be seen mouthing Rachel’s (Jennifer Aniston's) lines as she says them.
— Halo (@EatMyHalo) March 18, 2018
A momentary brain fart perhaps? A glitch in The Matrix? Who knows.