It looks straightforward — but that's an illusion. There are a lot of traps in this spec.

My arms looked huge in the mirror — I thought it had to be an illusion!

Does the data in that report only look like it's gone up, or is that an illusion?

She said she saw it, buzzing with excitement over an optical illusion.

He said "I understand," but there's nothing more dangerous than the illusion of understanding.