Actorsqu

This is initialized to -1. It's the actor squished... the actor that you are stepping on when they are shrunk.
When knee_incs is > 0 then the player is made to face the squishee. The actor is actually killed when knee_incs reaches >15.
In multiplayer, you auto-squish other players who are shrunk. This is done by setting:
knee_incs = 1;
weapon_pos = -1;
actorsqu = ps[otherp].i;
This is also set by the CON command pstomp.