Assertion: zombie's flag | /r/HasProperty | two flags per wave
Facets:
Source sentences:
text: The normal modes last five waves, hard modes last ten flags (two flags per wave), and Survival: Endless continues indefinitely until either the zombies eat the player's brains or the level is restarted.
text: This time, the player must survive ten flags (two flags per wave), with the zombies changing every two flags.