Giraffes are very tall animals, and tall animals have high blood-pressure. This means that mating is hard work for the male, and as such he checks first to make sure the female is in heat. How?

Explanation

Giraffes are very tall animals. As such, the actual mating ritual is hard work for the male. Therefore, he will first rub the back of the female with his head to provoke urination and then taste her urine. If it is ok - i.e. if he can taste that she is in heat - he will start courting her by following her around until she lets him mount her.