A greeting is a thing we do or say when we want to let someone else know that, for better or for worse, we've noticed that they exist.
It's also a nice way or a mean way to let someone know that you cared in some way that they're here. Whether you continue to feel that way depends on how the person you greeted responds to the greeting.
Nice or mean depends on how you point your finger and which finger you used or how you used it (E.G. by showing, pointing, pulling the pin on a grenade, the trigger of a gun, or pushing into their eye etc...) or if any fingers are involved. Usually the more fingers are involed, the friendlier the greeting. E.G. A finger is sometimes considered rude or mean, as is two if you're showing the butts of your fingers (do fingers have butts?) But three can be the number of coffee/beers you want at the table, four is even better and one more gets you a high-five.
Or a slap, which results in what I shall call the Schrödinger's Five. It is both a high-five and at the same time a slap, but you don't know which until felt.
It's not really a paradox though. I mean if your greeting involved a finger, depending on how you showed it and/or which orifice you jammed it into or if any orifices are involved, we can usually determine whether the response to that greeting will be a high-five or a slap.
If you have five more fingers and a palm involved, you can turn that into a clap.
Clap and slap have the same number letters and almost the same ones, but mean different things. A clap is a slap to your other hand that you repeat to make noise and cause both to hurt. This is a kind of self-sacrifice to show that you will endure pain and be noisy to greet someone. That's a very nice gesture. Unless you're clapping if they're being taken away in official-looking bracelets; then it's a mean gesture.
Hopfully you have two hands for a clap or, if you're holding onto something or lost one to a koala bear, you can use a table or your own leg. The top of your thigh, not the sole of your foot, unless it's facing your face. If it is, you should see a doctor.
You can use the five fingers and the palm of someone else's hand to greet another person, but you should ask nicely first. Start by greeting them.
Koala bears don't usually eat hands and actually aren't bears.