The “Helmholtz resonator” concept explains the frequencies of sound produced by clapping the hands together in different configurations.

“I had a unique angle and was able to put Speaker Pelosi right over the president’s shoulder,” he tells PEOPLE. “It was a clap that was gestured right toward him [Trump],” Mills recalls.

Hand clapping is ubiquitous behavior for humans across time and cultures, serving many different purposes: to signify approval with applause, for instance, or to keep time to music. Acousticians ...