It’s an interesting technique that is used by many filmmakers, probably most notable by directors like Stanley Kubrick to create a very specific look to his films. Forced perspective is the art of making things appear larger or smaller than they really are. In this video by Filmmaker IQ, we look at the actual science and math behind forced perspective. By using a model in a martini glass (shaken, obviously) we learn how forced perspective actually works.
Source: Filmmaker IQ