In the Options/Difficulty levels:
Music and sound : In here you will be able to turn on/off the music and the sound effects (sfx).
Joystick 1: This option enables a second player to play with the joystick. Click on it to enable or disable the joystick.
While playing, those options are available:
shift-P : Start music.
shift-S : Stop music.
Space bar: Pause the game.
Escape: Stop the game.