Originally Posted by Incredible Hans
I have the same theory. I agree with you that they looked as if they were dead and that, of course, there is a Thanos-Death-connection.
In addition, when Black Widow stabbed a Chitauri (the pilot of the vehicle she took over), no blood came out of the body. Like stabbing a corpse.
I would guess that they were not supernaturally re-animated like zombies(well, most zombies) but rather like Frankenstein's monster(though probably without being pieced together with body parts from different bodies); by science, albeit advanced alien science. Thus their bodies still have to function based on the laws of science and if you stab one and render their body inoperable then well they're not gonna be able to function.