Sacs are zerg aerospace insertion craft. Their terran analogue is the drop pod.
Sacs deploy units onto the map like drop pods. In campaign missions they deploy zerg units, even if the main zerg bases are destroyed, entire Hatcheries and buildings, and creep tumors off of creep.
Heart of the SwarmEdit
Sarah Kerrigan can summon sacs that delivers 40 primal zerglings, 5 primal roaches, and 5 primal hydralisks.
The unit plays two sounds, but the animation must be slowed to hear both individually. The distance that eggs are ejected upon landing decreases as the animation speed decreases.