Answer: a good, sharp sword.
In the Book of Judith, Judith is a hot widow who wants to save Israel from the Assyrians. So, she cozies up to the powerful Assyrian general Holofernes, who really wants to tap her Lord-Enhanced Loveliness. When she finally agrees to party with him one night, he gets super drunk and passes out, and she takes the opportunity to behead him. Really, it’s a lot like the story of Samson and Delilah, except the powerful idiot who can’t keep it in his pants is considered a villain, and the lady trying to murder him is the hero. Also, Judith was intelligent enough to realize that 99% of the time, beheading is more effective for permanently stopping someone than tying the guy up with bowstrings.
The Judith-Beheading-Holofernes story was apparently quite popular in art for many years. Of the ones I’ve found, this one by Caravaggio is my favorite, for the sole reason that they all have fantastic facial expressions.
Judith Beheading Holofernes, Caravaggio, c. 1598-99 (Source)
First, the beheadee:
That is certainly an appropriate face to have while being beheaded, although I thought he was supposed to be unconscious, which was how this whole thing came about. I guess his neck looks to be sort of three quarters severed at that point, which probably took a few whacks, so maybe he woke up when he had been liberated of a few tendons?
Also note the spurting blood that resembles party streamers bursting from a horrible piñata.
Judith's expression is even better, holding the head at arm’s length and looking a bit grossed out by the whole prospect, like a Jane Austen heroine tasked with pig-slaughtering duty.
But the person most excited in this scene is Judith’s servant.
This little old lady is ready to go with her head-transportation sack, fists clenched with anticipation, saying “Yes yes yesyesYESYES MURDER THAT #@$@# REAL GOOD!!”