The best thing about IR, to me, is how a woman's body responds to BBC.
I always imagine wife or GF being a bit shy and apprehensive about fucking a black guy, but once they start, she can't control her reactions.
Nipples get hard, and there's that hiss or loud inhale of air when he penetrates her pussy, soon followed by the sounds of her pussy getting very wet and juicy, and that leads to her cumming and squirting multiple times.
Hearing her verbal praise of his prowess and size, confessing her pleasure, and her encouragement to him are closely related, but actually hearing his big cock stroking back and forth in her pussy because she gets so wet is where it's at for me.