I'm looking for a resource to figure out how to program a function to cut a 3d model in game.

Example: Enemy/NPC is sliced into 2 pieces with a sword. His body is not hollow, you can see bloody texture where normally a 'polygon hole' would be.

The first step is to actually 'cut/slice' the model, then add in polygons to fill the hole in the model. I know this can be done in 3D modelling software, but I'm not sure how to go about doing this in a game, code-wise. I do not wish to use 'pre cut-up" models, the code will determine where the cut is.

Any pointers in the right direction would be greatly appreciated.