I like that in japanese porn, when there is maths on a blackboard, it actually is high school maths. Unlike in american porn where people looking old enough to be in university fucks in front of kindergarten level maths...
That's a correct proof that sin'(x)=cos(x).

Arkan321 said:

I like that in japanese porn, when there is maths on a blackboard, it actually is high school maths. Unlike in american porn where people looking old enough to be in university fucks in front of kindergarten level maths...
That's a correct proof that sin'(x)=cos(x).

That's because the japanese still have a plot to follow in porn

In western porn, if you mute the audio the "gimmick" is gone and it becomes regular porn