I always have the Kamasutra on my phone for some reading when I'm bored, because it's actually quite funny:
The author(s) categorize(s) the male and female sex organs into three categories according to their 'physical properties'. Those categories are then related to animals, i.e. the elephant for the 'well-hung' male and the antelope (IIRC) for the tight female.
When an 'elephant' engages into intercourse with an 'antelope', then they called an engagement of the highest order. But when it's the other way around, it's considered to be lowest order.
The author(s) also suggest(s) adolescent girls to 'train' with each other to be able to please their future spouse.