Rosenberg the alien

has anybody ever wondered how Rosenberg actually died? Watching this movie again you'll notice that edgar stabs Rosenberg in the neck with his.. erm bug claw. later it's revealed that Rosenberg is in fact a tiny alien that lives inside a giant robot's head. anybody ever wonder how he actually died though? my thought was that Rosenberg required some sort of other chemical other than oxygen to survive, and when edgar punctured the robot body it ruptured his breathing mechanism somehow. so by the time "j" had opened up the head inside the morgue, he'd already lost a lot of before mentioned chemical, and was by this point dying. then after the head was opened he was breathing in nothing but oxygen which killed him.

It's only reason i can think of as to why he died.