A straight back is like a flat ass. Just makes you look sort of "bleh", if you know what I mean. Sexy body 101: Arch that back. You can't overarch it, in fact. Pop your ass out and get that back bent.
Here's a GREAT example.
The opening bit is cheesy but her arched back is hard to argue with. Fast forward to 13:10. Whenever you're fucking doggystyle, make sure you have this ski slope back going. Don't be the chick with the sloppy straight back and flat ass.
Here's another amazing example.
At the 6:25 mark, you'll see what I'm talking about.
And Lela Star (another AMAZING girl to pick up tricks from) shows us in this clip what you can do if you arch that back in the below video.
At 8:30 it's obvious how hot that is and then REALLY picks up steam at around the 9:00 mark. Fuck your guy like that and his mind will be blown.
So remember girls, arch that back!
Helping you fuck hotter than ever,
Cara the Sexpert.
