When the fate of something or someone has been determined and they are being watched. The predator's main thought is "SOON."
The origin of this phrase is in an under-appreciated lolcat, where an evil-looking cat is watching a chihuahua, with the only caption being SOON.
When pronounced, it helps to add suspense and drama by saying "SOON." in a low voice employed by that movie advertising dude.
Poppy, upon seeing Moolie loiter aimlessly: