Rawr! After a suggestion from PlanetPhillip for a combine-manufactured headcrab, I couldn't stop myself. It was originally meant to be a reskin, but I am a little girl who has lost her mummy at Cronulla beach when it comes to texturing (that means I cry), so I modelled instead. Luckily I have been fiddling with compiling animations onto existing rigs with custom meshes over the last few weeks and it was all fresh in my mind. This was also designed to slip straight onto the headcrab rig, so it was pretty smooth sailing in general. I think I might do a tutorial on this sometime soon.
Overall the model took me about four or five hours, the texture took maybe 12 hours and the source-related stuff took under two hours. It took me three days from first vert to finish, and that was working in my spare time between other more important models (more on them later perhaps). If anyone happens to read this and has any idea about how to package it so anyone can download it and plonk it in their map without overwriting the old headcrab, please leave a comment, I am really struggling to code this in.