Yeah I actually found that out from shooting trikes from behind a while back. Then I started trying it on Rex. You can do from between the tail and leg from the top through skull or from the top through the back. Of course you have to shoot at the correct angle so it hits the heart. It has been more fun trying to kill them that way because I miss more shooting from the front. Hahaha.

lol, thats new to me

Most people I think don't know there are more ways to 2 shot a Rex but I could be wrong.