Wind-Brahmin Wrangler

 is a unmarked Quest in Fallout: New Vegas.

Quick walkthrough
Approaching the cattle pen at Brooks Tumbleweed Ranch will uncloak a nightkin selling "wind-brahmin". His fee is all of your caps. If you don't buy them, he will become hostile. If you choose to buy one without asking how much, he gives you a stealth boy for free. A stealth boy can be pickpocketed from him, even if you received a stealth boy from him beforehand. Further interactions (insinuating that the tumbleweeds are not in fact "doggies") results in the nightkin becoming hostile towards you. If you buy a wind-brahmin, the nightkin can be killed for your caps. Just in front of the pen is a dead wastelander.

If killing the nightkin is too much trouble, it may be worth dropping some caps before the transaction for a "bargain" Wind-Brahmin and a Stealth Boy.

Sometimes the nightkin may not uncloak immediately but will eventually apear at a different location.