A XScream

A_XScream is a code pointer used in the explode animation for the Player and various monsters.

just plays the sound effect DSSLOP (the gib/exploding corpse sound).

Uses
The  code pointer appears in the following states in Doom's state table:

Example
The following is an example of how to set the  code pointer in a Dehacked file:

Pointer 21 (Frame 34) Codep Frame = 750

Or using BEX syntax:

[CODEPTR] Frame 1234 = XScream