There were lines of gibberish written in the script for Leatherface. Tobe Hooper would sit with Gunnar Hansen and tell him what the lines meant, and the actor had to figure out a way to say that without actually speaking. In the scene where the Old Man comes home and starts yelling at Leatherface about the door, Hansen remembers a take where he communicated a little too verbally. Hooper told him "there was too much intelligence in the character", and the shot was redone. "My one chance to have a line," says Hansen.
Marilyn Burns, whose character was chased by Leatherface through the undergrowth, actually cut herself on the branches quite badly, so a lot of the blood on her body and clothes is real.
The soundtrack contains no sounds from musical instruments (with the exception of some copyrighted music they had the rights to), instead they used sounds an animal would hear inside a slaughterhouse.
Gunnar Hansen originally turned down the role of Leatherface due to the sheer brutality of the plot. He was then persuaded by Marilyn Burns, who was friends with him at the time.