No, not food. He said he couldn't risk running out of food by having to feed a cat. At any rate, he didn't want to be slowed down by anyone or anything. I lost a lot of my respect for him when I read that. To me, our humanity is largely defined by our treatment of the so-called "lower" animals. To Shackleton, the cat was expendable. Very cold-blooded, I think. I watched the special on the expedition, and it was pretty obvious the cat was killed because Shackleton didn't want to bother with it.