"Shoot the big ones"

Enemies of the Tyranids have learned many valuable lessons at a terrible cost in lives lost 
and blood shed. One of the most important stratagems has been teaching troops to pick the 
right targets from the swarm even in the heat of battle. Because of this an opposing player 
can freely choose to direct fire from his units at any Tyranid brood or creature within 
range in the shooting phase, line of fire is only blocked by terrain and vehicles.