It's abundant in the film. The wolves can pop up from anywhere at any time. This is much more apparent in sequences where the wolves are out of view and are killing people.
The sequence where the zookeeper is on his motorcycle and he can hear the wolves all around him and he's trying to get away. He goes through a tunnel and you think he makes it when a wolf comes out of nowhere like a rocket and knocks him off the motorcycle.
In order to lure their human prey towards them the Wolfen imitate the sound of a newborn baby, knowing people would be unable to resist trying to help a distressed infant.
The climax scene with Wilson and company surrounded by the Wolfen. Also, if you look at one shot of the pack leader atop the bus, when Wilson's partner is going for his gun, the way the wolf's mouth moves almost resembles a smirk. Yes...a wolf with a Slasher Smile...brrr!
