Matthew Weathers is a math professor at Biola University, and he likes a good gag. For April Fools' Day this year, he played the prank below on his students, in which his "shadow" on a projection screen started to misbehave. All sorts of interesting stuff begins to go down, including manipulation of a computer desktop, and even removal of the desktop entirely, allowing us to "see through" the projection screen to the blackboard behind it. Ultimately the president of the university has to step in and take care of the shadow. Check it out:
For more context, this appears to be part of a discussion of Flatland, a book about interaction between different dimensions (as in this video, the 2D shadow interacts with the 3D world of the professor). You may also enjoy Weathers's Halloween prank from 2009, again related to Flatland. You can actually read Flatland online (it's in the public domain) if Weathers has sparked your interest!