The eye contact as he slides his fingers through the opening and into your throat, testing your gag reflex. The slight smirk of approval when you don't flinch. Delighting in how wet his finger is from your open mouth. His other hand firmly pinching your right nipple. Pulling that little bud hard till you feel pain.
Can you see the lust and desire in his eyes? You already know he is going to use your mouth. I wonder what devilish things he would do. So many possibilities with a open gagged mouth. How would you feel if your 'Sir', after his fingers felt the back of your throat, sucked his own fingers, licking off your dribble and saliva? Would that make you pant a little? I think it would.
I think you'd love him to lick the little bits of dribble that trickle down the corner of your mouth. Knowing you don't flinch and can deep throat makes him hard. You can tell by the look in his eyes that he's going to see if what you promise can be fulfilled.
The open mouth gag exciting him more, knowing that you can't prevent his hard cock thrusting in your mouth and down your throat. That you're putting your trust into his hands, which already are grabbing your hair and pushing you to your knees.
When you see how hard he is, that single drop of pre-cum already on his cock head, how you want to taste it. You can't speak properly, your sounds not making sense. But he knows instinctively. He holds your head back, dangling his hard cock above you. With his free hand he squeezes that drop out. Your tongue begging for it. That single drop, so sticky and sweet.
A single drop, how the drip becomes a strand, reaching your tongue and connecting you to him. The slight salty taste, but delicious. You want more. If you could you would beg, but the gag prevents you. That desperation in your eyes. You want him to use your mouth as a vessel to fuck. He obliges.