A photo online has left people scratching their heads searching for the THING that is meant to be wrong with it.
In the foreground are a few friends, posing and smiling for the camera in shorts and singlets. Nothing about their clothes or faces looks like it shouldn't be there.
But the trick is to not look at them - but at the background. Spotted it now?
Every single person in the background has the same face!
How long did it take you?