A neat idea for more evilly-minded GMs... the concept that not all monsters just lie there quietly when those pesky player-characters kill them off but all manner of dramatic effects just might occur (to the discomfort of anyone attempting to loot the body, of course!).
First up, a simple mechanic to allow for this using a 'Death Effect Template' that can be applied to the monster(s) of your choice, adding +1 to its CR and setting the variables for whichever effect you decide is appropriate (or is the result of a die roll on the table of effects that follows).
Then comes the actual effects. #11: Ascension could give good-aligned parties pause for thought: "The corpse glows softly and starts to rise up. At 10 feet the corpse starts to fade away. An angelic choir can be heard." Ooops! Have they killed someone that really ought to have been left alive? I forsee fun with this... I have a 'good' otyugh tucked away in a sewer system I think I'll apply this one to, the party in that game have so far talked to him rather than slay him out of hand, but anyone going for him is in for a shock now!
Of course many of the effects give a shock of a more tangible nature. I quite like # 37: "Explosion (Rust) The corpse explodes and anything within range that could rust immediately does so." There are other kinds of explosion, acid bursts and even electrical discharges to choose from, as well as a fair few disquieting effects than do no lasting harm but you can have a lot of fun with the players until they do wear off...
A neat little resource, to be used sparingly for best effect. Catch those looters unbewares!