Aliens no beam?

Game is great just like that other game many of us grew up with but this game is unique in its own way,anyway 1thing is how I remember is missing I dont quite know what its called but its when the alien comes down an drops the beam down and I forget if you supposed to go in the beam or stay away from the beam this happens all during the game those beams come down,can somebody help me out.great game THANX.

th 30 pack about Alien Swarm, v1.12