Howdy grapplin' pardners. Today we're talkin' like cowboys 'cause we're focusing on the lasso hook/guard (and, because we're idiots). There's lots of good grapplin' in the lasso, and you should definitely partake in it if you haven't already.
Likewise, there are many a ways to get yerself a triangle from the lasso position. The one featured below is probably the most complex, difficult and least direct. At the same time, it's that kind of complexity and nuanced movement that is often needed to catch a skilled opponent who is well prepared for a straight-down-the-middle attack. I'd deem this an advanced move to say the least. If you are not already a seasoned and well-conditioned triangle choke attacker, you may want to wait to walk before you crawl. But, if you've got it down, then proceed.
Note: Yes, this is a sport BJJ-specific technique, as are many techniques that require inversion. It's highly unlikely that you'll encounter an high tech grappler in mortal combat on the street. You never know though.
Note 2: Thanks Shoyoroll and thanks to Victor Siverio for the top-notch illustration.