The pushbutton isn’t a normal push button, but rather two wires next to each other that if you touch the tip of your finger to it creates a connection between them via your fingertip and if your finger has a resistance under 35kOhms it will turn on the circuit. If your finger is more resistive, the circuit will make a dimmer light and possibly run at a different speed depending on how sensitive astable multivibrators are to supply voltage.
