The autopsy for Knut is in—the celebrity polar bear drowned. However, Knut collapsed into the enclosure pool because of swelling in his brain, likely brought on by infection. It's unclear exactly what the infection was—rabies, botulism, and mad cow have been ruled out. Whatever caused the inflammation, it was severe enough that the examination team said Knut probably wouldn't have survived even if he hadn't collapsed into the pool. "Given the massive scale of the inflammation, Knut would probably have died sooner or later—it wouldn't really have been possible to save him," said Claudia Szentiks, a pathologist at the institute which led the examination. Animal rights groups had said Knut was traumatized by living in the zoo, but the team found no sign of chronic stress.