Next to "Off with His Head", snapping a person's neck is one of the surest ways to kill someone in media. Typical procedure: Alice stalks Bob. Catching him unawares, Alice grabs Bob's chin with one hand and his opposite temple with the other. Bob just has time enough for his eyes to go wide with the realization of how screwed he is when Alice wrenches his head to the side with a hideous cracking of bone (a walnut cracking was used for this in Faster, Pussycat! Kill! Kill!, which may be one of the earliest examples). Bob is always killed instantly and almost always with his eyes open. Sometimes Alice at least appears to put in an effort (or has superpowers or something) but often is remarkably blase about it.