It may be the most famous cartoon to ever grace a TV screen, but 'The Simpsons' is more than capable of the odd blunder, too.

One of the show's producers, Matt Selman, pointed one of them out the other day and it's been tickling people on Twitter ever since.

In the episode 'And Maggie Makes Three', there is a scene where Marge is telling Homer that she's pregnant with their youngest.... except there's already a picture of Maggie on the wall behind them. Oops.

Peoples' reactions have been as you may expect - including some of its stars: