Remember #TheDress from last year? Well, banish that from your memory because there's a new optical illusion doing the rounds on social media that will make your brain hurt.
BBC trainer Marc Settle stumbled across this mind-boggling phenomenon while packing away his son's wooden train track.
In a video shared on Twitter, Settle writes: "My toddler's train track is freaking me out right now. What is going on here?"
The clip shows two track parts stacking directly on top of one another... despite looking like they are of totally different lengths when placed next to each other. Crazy or what?
Twitter had some rather interesting theories...
Settle later tweeted to say this puzzling illusion has a name and an explanation to go with it.
The answer, as the Jastrow Illusion explains, is all about perspective.
For those who are wondering, the two pieces of track are actually the same size - despite looking different when placed next to each other.
However, because of their shape (the way the tracks curve) and the angle at which they are placed, the segment at the bottom of the screen appears bigger when placed side-by-side - because the short edge of the upper track is being compared to the long side of the lower one. Makes sense now?
You can now breathe a sigh of relief and go back to daily grind.