"In the 'Four Horseman' cue, the bass drone you hear in the beginning is the contrabass clarinet, and it creates all these weird squeaks and noises and harmonics," Stefánsdóttir said.

Source: https://www.slashfilm.com/1188474/this-instrument-provided-the-sound-of-terror-in-the-knock-at-the-cabin-score-exclusive/

Others are more adult, such as the squeaks of the Galimimus, which came from a female horse excited by the presence of a male.

Source: https://collider.com/jurassic-park-facts/