A sexual maneuver wherein one is having sex with a female vaginally and doggy-style, and one inserts both thumbs (or two or more other suitable digits) into her anus and crooks them on the inside so as to create a solid lock. This creates the possibility of pulling the girl onto you more forcefully and with greater sensation. To say the least.
"Boarding parties away! Launch the grappling hook and bring her alongside for us to plunder!"
by Der Kaiser December 19, 2004