Sound similar to a loud clicking clock that is usually attached to a timed bomb is produced by this circuit. Use this circuit for fun, don’t use it for terror. The 200k pot adjust the frequency of the tick. By charging the 2u2, the circuit starts and when 0.65v is on the base of the NPN transistor, it starts to turn on. This will turn the 2N3906 on and the voltage on the collector rises. This pushes on the small charge the 2u2 into the base of the 2N3904 to turn it on more.
When the negative end of the 2u2 is above 0.65v and now the electron starts to charge in the opposite direction until both transistors are fully turned on, this will continue. Less current is received by the 2N3904 into the base and it starts to turn off. Both transistors turn off very quickly and the cycle starts again.