Hard to explain, but it is that fleeting, unsettling moment when the hero/heroine just knows the killer is aware of their presence.
Halloween had a few examples:
There was a similar scene in Jeepers Creepers as Darry and Trish drove by the Creeper's church as he dumped a body. He stopped and watched as they drove by:
Something about going from that eerie, 'something's-not-quite-right' feeling to actually connecting with the maniac on the loose just gives me the creeps!