Flam is the first bug found in the meter family. Flam is a new drummer in the house. Flam gently taps on paper producing percussive and scratchy sound. In full sun, flam tapps on the paper strongly and rhythmically.

Flam -- one of the basic patterns (rudiments) of drumming, consisting of a stroke preceded by a grace note

Flam uses the schmitt trigger oscillators like many other bugs to create the pulses, which will result in the tapping patterns. Output of the oscillator send the voltage to the transistor that turns the meter on and off. Article on this experimentation and be found here.