Smiting

Smiting is a powerful ability where a being kills another being by touching them.

Angels can inherently smite demons, monsters and humans. Archangels and seraphs can smite demons effortlessly and kill them instantly, but, for regular angels, it takes more concentration and if they are too physically or mentally weak, it will not work and they will only be able to smite black-eyed demons but not high-tier ones, such as Alastair. It is implied that an angel cannot smite a demon out side of a vessel, as Castiel pushed a demon back into its host, while trying to escape, before smiting it. If a demon or human has been smote, the vessel's eyes light up with a white holy light, burning the eyes and killing the demon. Apparently, Angels can control how powerful their smite is, and can choose if it will kill them, or simply burn out their eyes.

Another form of this smiting is displayed by Sam Winchester multiple times, most notably on Lilith and Alastair, only after drinking much demon blood. This demonic version seems to make the demon glow with yellow light that illuminates the skeleton - similar to the Colt and thedemon-killing knife - then the demon and vessel die.

Sam Winchester can smite a high-level demon Alastair by just using his mind after he drank a lot of demon blood.

The demon Cain displayed a similar power except the light was red instead of white.

When a Knight of Hell is killed by the First Blade, the demon acts like it has been smote by an angel or Cain rather than the usual brief glow other demons have when they die, even those stabbed with the Blade.