Depending on experience with more demanding anal workouts due to very girthy dicks, very deep digging or DAP-ing some girls stay pretty motionless during reverse cowgirl anal/dap insertions, others throw their head back in an iconic reaction or have their eyes popping out almost, some clinch their hands etc.
I'll try to explore some of the more surprising reactions - authentic ones on that thin line of lust and pain as well as just acted reactions to meet porn users demand to celebrate a difficult porn sex act.
I'll start with a casual reaction by Alicia Trece in her Boys Casting scene @ GIO2225
(https://pornbox.com/application/watch-page/201969). Its about 15th DAPs in her porn career so she doenst really care much for it anymore. It shows a pretty indifferent approach, but its ideal to show livelier reactions starting from this point.
Alice acting very casually for that New Boys Casting test round, first forgetting to show some DAP insertion reactions, but than doing it still for him rather than the camera. LOL!