“When you see a one-eyed cat, spit on your thumb, stamp it in the palm of your hand, and make a wish. The wish will come true,” says an American superstition.
From what I’ve read, the one-eyed cat used to be associated with witches because “the Evil One could create nothing perfect.” And saliva was believed to act as a medical and magical prophylactic against sores, growths, and the Evil Eye. So perhaps spitting on your thumb and stamping it in the palm of your God-given hand reversed the evil, unlucky omen of the one-eyed cat and gave it power to grant a wish. Just a guess.