When we were very young we were shown the ‘two noses’ illusion by my Dad.
If you cross your fingers and touch a small object (such as the tip of your nose), there will seem to be two of whatever it is. Not being able to see the object strengthens the illusion, and because you can’t see the end of your nose very well it is a suitable tactile target. Besides, using your nose is amusing.
This illusion has been known for at least two thousand years. Aristotle wrote (Metaphysics Book 4):
“… touch says there are two objects when we cross our fingers, while sight says there is one”
It’s an example of a tactile illusion. There are a lot of optical illusions known but illusions of touch are less common.