Spielberg was inspired to do this shot after listening to an Earth, Wind, and Fire song in his car, which caused the mirror to shake.
So Special Dinosaur Effects Supervisor Michael Lantieri had to find a way to recreate this onscreen.
"The mirror shaking was really very easy ... but the water was another story," Lantieri said in an interview from the "Jurassic Park" Blu-ray. "It was a very difficult thing to do. You couldn't do it. I had everybody working on it. And finally, messing around, with a guitar one night, I set a glass, I started playing notes on a guitar and got to a right frequency, a right note, and it did exactly what I wanted it to do."
To replicate that for the shot, they "fed a guitar string through the car, down to the ground, and then I had a guy lay under the car and pluck the guitar string," Lantieri said in another interview from an early "Jurassic Park" DVD.