It'd be cool if lesser enemies could have fear struck into them, so you have to chase them down while they're screaming, and shouting to others stuff like "RUN, RUN, AHH!" (Lol), and the more people you scare, the more marines/others will come and try to kill you. (And if it was in a city, you could cause so much fear, and have enough aliens with you, that the government puts martial law on the city!!)