Yaaaaa-Hooo!
 

A blonde girl is driving through the West. Her car runs out of gas and an Indian comes along on a horse and gives her a ride to a gas station.
Every few minutes he lets out a wild whoop that would curdle milk.
Finally, he drops her off with a final "Yaaaaa-Hooo!," and gallops off.
"My god!" says the gas station guy, "What the hell were you doing to that Injun to make him holler like that?"
"Why, nothing," says the blonde, "I just sat behind him with my arms around him, holding onto his saddle horn."
"Lady," says the guy, "Indians don't use saddles."