Purely History on Instagram: "The voice of Boo in Monsters, Inc. (2001) was performed by Mary Gibbs, who was only around 2 years old during recording. Since she was too young to read or follow a script, the Pixar team recorded her natural reactions while she played around the studio. They captured her laughter, babbling, and spontaneous chatter instead of formal dialogue. Editors then carefully stitched those moments together to create Boo’s lines, resulting in one of the most genuine child perf