Demon Attack (Atari 2600)- Canon (music) (Wikipedia)
In music, a canon is a contrapuntal (counterpoint-based) compositional technique that employs a melody with one or more imitations of the melody played after a given duration (e.g., quarter rest, one measure, etc.). The initial melody is called the leader (or dux), while the imitative melody, which is played in a different voice, is called the follower (or comes). The follower must imitate the leader, either as an exact replication of its rhythms and intervals or some transformation thereof. Repeating canons in which all voices are musically identical are called rounds—familiar singalong versions of “Row, Row, Row Your Boat” and “Frère Jacques” that call for each successive group of voices to begin the same song a bar or two after the previous group began are popular examples.