You are looking at your glass and you see strange images on your beer mat?
Don’t worry you’re not drunk. This is called an anamorphosis. It is a distorted image, which is only seen from a certain angle or with a specific optical device and in that way looks it realistic.
Puzzle two of our coasters together and discover a hidden drawing. This dates from the Renaissance to show in secret, often prohibited, slightly erotic pictures, this was the first form of eroticism (perhaps we may even speak of the first kind of ‘porn’.)