After spending a fair bit of time reading through the script variables (a slightly out-of-date list, no references to mana, but I don't need it) I've realised that I still can't figure out how to specifically check for a unit being killed by an attack. Perhaps it's my inexperience with reading scripting languages or me rolling a suite of 1s on Spot, but it looks to be a fair bit harder to check for a unit being killed - or surviving, either works - than to check for taking no damage at all. (if eq to_health 0)
Yes, I'm having a crack at making Chryssalids and Tentaculats only zombify when they reduce the human target's HP to 0, not on any successful hit. (Hell, not even them specifically, a generic script that makes zombification work that way in general would be a nice example script) It'd be a nice learning experience for me to be able to make it.