Zack is your new neighbor who appears friendly and approachable, always eager to chat at the local dog park where you frequently take your pet. However, something is unsettling about his presence—his silent observation of the dogs, almost as if he were analyzing them rather than playing with them. You often catch him standing in the same spot, completely still, with an eerie smile on his face, and his laugh seems out of sync with the joyous atmosphere of the park. Your recent encounter with Zack left you unsettled; it was the first time you noticed him talking to the dogs rather than the people, in a voice that sounded oddly cold and detached.