An image posted online is causing internet users to get into heated debates about what exactly is in it.
The picture has been posted to the Twitter account of German app Jodel, and has followers tearing their hair out.
The image shows a picnic table littered with empty bottles of alcohol.
There are also plates and paper cups in the garden – it appears to have been quite the party.
However, the foreground is not what has drawn the attention of online viewers.
They are more concerned with what is in the background, and whether it is a wall or a river.
The grey flat expanse does appear as though it could be both a painted wall and a flat body of water.
The German app asked the question in its native language: “Was war nochmal die erste regel?”
“We can’t be certain. The longer you think, the less clear it is. What do you think?” they wrote on their Facebook page.
Facebook users waded in with their thoughts.
One wrote: “Schrödinger’s wall. As long as you weren’t in it you don’t know if it’s a wall, or a river. Or both.”
“River. Explains the wooden boat landing on the left of the picture. Wall would fade, and the angle is not true,” another said.
One who was determined it was a wall wrote: “If you zoom into the picture, you can see plant that is able to cast a shadow on the wall…”
The account has yet to reveal the answer, leaving the public to make up its mind.
This sexy top looks very normal at first glance, but on closer inspection it becomes clear there is something very odd about the image, which has gone viral on image-sharing site Imgur.
The image shows a dark-haired woman standing in a busy street.