pay

This is a directional sign.
Think of having a coin in the palm of your left hand. You place the tip of your right index finger on or behind the coin then flick the coin to the person whom you are paying.

pay:

"pay him/her"

"pay me"

"owe a debt"
The index finger jabs the palm twice as if saying, "Look, it says right here that you owe me money!"

Question from Scott: "Investigate" looks a lot like "pay" to me. I guess the difference must be the orientation of the right hand. For "pay" the finger is flicked back-handed, whereas "investigate" has a palm-down orientation. Plus it repeats. Yes?

Bill: Yes. The angle of the index finger to the palm when doing "investigate" is similar to the angle of a wood chisel to a piece of wood. Investigate uses a double motion that is similar to quickly sliding a penny about four inches along the surface of a table. Sort of a "digging movement." The movement continues off of an inch or two beyond the tips of the left hand fingers. Also, "PAY" is directional (you-PAY-me, me-PAY-you) but "investigate" uses a separate sign for the subject-object relationship.