Despite its remarkable special effects (for the time, that is), one of the most difficult scenes to achieve in Jurassic Park was the movement in the glass of water into the Ford Explorers as we approach the Tyrannosaurus Rex.
Spielberg directed the special effects producer (Michael Lantieri) that were concentric circles. But Lantieri could not come up with how to achieve it. Playing guitar at home, Lantieri noticed that the strings generated the effect in a glass of water. The next day the scene filmed by installing a guitar string inside the vehicle.
Another curiosity of the same scene is that the dinosaur latex absorbed too much water, making it heavy and difficult to handle, so we had to cover from the rain without being noticed.