It keeps her off balance and makes her more pliable. After a few disorientating slaps you'll suddenly find you're getting deeper into her throat. Slap! And a bit deeper ... slap! slap! ... you're now an inch further in than before ... slap! ... and before you know it those last few crucial inches have been achieved and you're fucking her face at full depth for the first time as the tears start to fall, her unseeing eyes stare blankly out, and you prepare to explode in her helpless throat ...