When Marc Blank-Settle stacks the track parts on top of one another, they look like exactly the same size.
But when he puts one track in front of another, one looks much longer.
"My toddler's train track is freaking me out right now," Blank-Settle wrote on Twitter. "What is going on here?!"
The video, posted on Wednesday 6 April, was retweeted more than 2,000 times in two days, with many commenters attempting to offer an explanation to the illusion.
Others were too confused to try and work out what was happening.
According to a number of people on Twitter, what's happening here is a Jastrow Illusion.
In these illusions, named after psychologist Joseph Jastrow. objects can appear to be different sizes because the short edge of the upper object is compared to the longer side of the lower one.