Two people who have just come to some sort of agreement both spit in their palm and then shake hands with the wet hand. Basically, this is the "lite" version of a Blood Oath. However, it still conveys utter seriousness that is many steps above a Pinky Swear. Plus, it avoids the horrors of showing an actual Blood Oath. And finally, it happens in real life, so it's hardly unrealistic. It's often used by children, country "bumpkins" (who are probably not as simple as they are assumed to be by the other party to the agreement) or members of certain cultures, like Roma and Irish Travellers.