Ok i saw a trailer and will be dad gummed if i can find it now.
People would be walking in large public areas like a mall or a college campus. Everyone would stop and attempt to be very still and show no emotion. Then these large white alien phucks would come by and basically come up and sniff, rather get real close to certain people Reading them to see if they were towing the alien line or were being human. Its NOT the one with Nicole Kidman. Perhaps similar theme, but this one was.
Ok this is not the alien but the alien kind of looked like this only White: