Thought really doesn't have to be a part of arousal at all. In my opinion, the rational pattern we place on arousal when we try to concentrate on it damages the 'build' of sexual tension. Release comes when the body surrenders to natural, prime instinct.

I think the bondage and most "forced" play stems from a primal place, where we answer instinct to take what we want and revert to animal sensation, or be taken and submit to those feelings.

And I think that's the fantasy from top and bottom views; the top takes pleasure by force, and, will succumbed to imprisonment and brutality, the bottom survives by finding pleasure in surrendering the body, mind and soul to the aggressor.

The orgasm can come from forced stimulation, but I think there has to be the element of submission of will first. In some of the better stories, it takes a while to happen, but it does happen.

Happens in nature (specifically with wolves), but there's a tenderness that couples it. Humans have the rationale to build in "evil" in sexual abandon and "good" in chastity. Animals just do their courtship dance, then struggle to fulfill their gender roles as instinct directs of them. The male provides for the female. The female protects the young.

For me, that's the only reason I can think that Bestiality is as popular a subject as it is-- that it strikes that sleeping animal instinct that we bury under our rational superegos.