Thank you so much for this lesson! My students loved it!
I went ahead and tweaked it a bit for my High School (and my own style).
First I introduced optical illusions, showed examples, then a video.
Then I talked about riddles, gave examples and had a riddle race.
The riddle race was an idea from another lesson I saw on Waygook.
First, I cut out the riddles from my riddle list.
Students are in groups, and I give them riddle number 1. Everyone tries to solve. The group will tell me the answer, and I will give them riddle number 2 if they are right. Then riddle number 3, and so on.
Whoever gets the most right at the end of class will get candy. :D
We only got to around riddle 11 in class.