Why did Jurassic Park build dinosaurs you could touch?

Because a real machine moving in front of the camera has a physical presence that a picture added later does not. An animatronic is a puppet controlled through electronics so that it moves fluently, and the word blends animate and electronics. Its main advantage over CGI and stop motion is that the creature is physically there, moving in front of the camera in real time. Steven Spielberg wanted full-scale dinosaurs on set as much as possible, rather than the stop motion common in older dinosaur films.

He turned to Stan Winston, who had declined to work on Spielberg's E.T. a decade earlier and regretted it. This time Winston said yes, even though he had no idea whether his team could build animatronic dinosaurs. They made fifth-scale models, cut them into cross-sections, and expanded each into a full-size version on a robotic frame, with latex skin on top. The T. rex stood almost 20 feet tall and 40 feet long, and the biggest animatronics weighed 9,000 pounds. Paleontologist Jack Horner called it the closest he had been to a live dinosaur.

The machines needed hidden helpers: sets were built on raised platforms with the mechanics underneath, and puppeteers, pneumatics and underground cranes made the creatures move. The venom-spitting Dilophosaurus was worked from a trench in the floor, using a paintball mechanism to spit a mixture of methyl cellulose and K-Y Jelly.

In the end, the 127-minute film has 15 minutes of dinosaur screen time: nine of animatronics and six of CGI.