Lot’s a questions here, huh. In watchin’ this scene about a million times, one thing becomes really glaring – how did Jack know that Ennis’s hand was going to be where it was when he reached out for it? We first see Jack, lying on his left side (facing away from Ennis) under the bedroll. He awakens, pushes back the bedroll (still facing away) and begins reaching out with his right hand
behind him. Remarkably, his hand lands virtually spot on Ennis’s right hand that
just happens to be lying outside the bedroll. He grabs it and - away we go. How did Jack know the geography of all this in his sleep with his back to Ennis in the dark? Try it sometime. Why didn’t he think that Ennis would (like Jack) have his hands
under the bedroll for warmth and head in that direction? Of course that wouldn’t have worked very well on camera, and these guys again make it all look so believable partly by the effective and engrossing fast action that immediately follows (the tussle, grabbing, head butting, and caressing).
I’d agree with loreen here about Jack’s “priors” too. Like you say, so much in the film is “cunningly put as innuendo” so everyone can draw and develop their own conclusions based on personal experience and desires. A terrific way to make individuals a part of the experience -
if you can pull it off, and Ang certainly did. My personal feeling is Jack was just lookin’ for some “buddy fun” of a more limited nature, and, as Ennis had admitted to not yet “having the opportunity”, Jack was going use this circumstance to provide him an opportunity. Not calculating that Ennis (who had never driven before

) would necessarily go “full throttle”. Think he quickly realized that Ennis was like a stick of dynamite, once lit you couldn’t put it out.