The choker appears in the map "Left 2 Die" as a zerg NPC unit. It is more offensive-based than the infestor, capable of engaging enemies directly. It has a tentacle attack that shoots up to 2 tentacles that drag targets towards it, doing damage over time.
The choker's tentacle ability makes it highly dangerous against lone units. The units are first hooked by a tentacle similar to the Neural Parasite which drags them toward the choker whilst incapacitating and damaging them. The unit is only released if the choker or its prey are killed.
While the choker's tentacle attack makes it dangerous toward lone units, and its attack out-ranges both bunkers and planetary fortresses, a simple counter is to place a marine or SCV behind a bunker with a medic or two. The choker will move to grab the unit with its tentacle, opening it up to fire from the bunker.