What does Ralston realize about his arm that causes him to panic and wildly thrash around trying to free himself?

Ralston cuts his thumb and in doing so, he sees the decomposition of his hand. Noticing for the first time the degree of decomposition, it sets him in a panic that the poison travels up his arm. Ralston accepts losing his hand before, but to lose his entire arm and more sets a panic that he does not handle well by day six. As soon as he sees the hand, he feels that it is not his or a part of him and wants nothing more than to rid of it.