The monster spawner attempts to spawn 4 mobs at randomly chosen points within the spawning volume, then waits anywhere from 200 to 799 ticks (10 to 39.95 seconds) before spawning again. As it waits, the mob model inside the block spins faster and faster. Except for the normal solid-block spawning requirement, all the remaining ones must be met (not in a solid block, correct light level, etc.), so the monster spawner often produces fewer than 4 mobs. When it does spawn, it emits a "poof", and more flame particles temporarily appear around it. If the monster spawner fails to spawn any mobs because it did not pick any suitable locations, it repeats this process every tick until it succeeds. It only starts the next wait cycle after successfully spawning at least one mob.