Goat........... human............. goat.............. human.
It may just be a sign of how diverse humanity can be when bisexuality can be seen as possible by some and not by (oh the temptation to spell it 'bi'...) others.
I had some bisexual friends at uni, they (both lads and ladies) engaged in relationships with people of both gender. some lasted, some didn't. It just seems that in this particular orientation gender is not a factor. Although, yes, species is still rather important.