Have you ever noticed that Rachel was replaced in a scene from this 'Friends' episode?

We are pretty passionate 'Friends' fans, but we had never noticed this!

Blogger Jordan D'Amico has just pointed out a mind-boggling blooper.

And now that we've seen it, we can't unsee it!

In 'The One With the Mugging' episode, right at the very beginning, Rachel was replaced by another actress.

Initially, Jennifer Aniston can be seen in the kitchen with both Monica and Joey, but when the shot cuts back to Rachel and Joey standing there together, it isn't Rachel at all!

BUT WHY?

That's something we'll probably never know...