@Grey: The first pannel say 'rush', as it is what the zerglings (type in the first pannel) are most known for, the 'zerg rush'. In the three other pannels, the zergling has evolved into a baneling, an explosive unit. Thus the 'boom' corresponds to the comin' explosion of our lil' ex-zergling.
First panel says "rush" and even the uninitiated should have at least heard the phrase "Zerg Rush" the second panel there is an obvious change in the zergling doing the talking, and now says "boom" so what is likely to happen to this zergling has been made fairly clear. I've never played starcraft.
