I'm going to use it in a scene where Zim is wounded by Nny during their fight. Luckily Zim gets better and manages to heal quickly.
Something I forgot to mention, In my version Irkens have a high tolerance for pain and can even regrow severed body parts, this includes being able to survive decapitation by regrowing their head. In short they are hard to kill.
You can use the idea of them having high pain tolerance and regeneration if you want to.