Optical illusions have long been a key part of the magician’s toolkit. Here’s a really good illustration of how and why they work.
BBC Academy trainer Mark Blanc-Settle hit the Twitter jackpot with a tweet on the “Jastrow Illusion” — the mistaken impression (embedded in magic tricks since time immemorial) that two objects that APPEAR to be of different sizes are in fact the SAME size. He had more than 3,000 retweets.
He uses the illustration of curved sections of a model railroad track, but you can find others as well.
Here’s the video he tweeted (the link is to Slate, where I found the story):
Here’s his Twitter page, which has further discussion of the illusion:
And here is Wikipedia’s explanation of the Jastrow Illusion