They can seem lazy, but they will also not put themselves in danger. A horse can be worked until it drops, but not so with a mule. Mules are very intelligent and it is not a good idea to abuse a mule. They will do their best for their owner, with the utmost patience. The mule is a sterile hybrid, meaning it cannot reproduce.
Mules come in both male and female.
A tiny percentage of female mules have had foals, but this is considered a freak genetic accident. Mules are a combination of traits of the parents with the most obvious donkey traits being long ears, narrower body and smaller hooves. The horse contributes size, speed and muscle. There are both male hinnies and females. The genetic inheritance of the hinny is exactly the same as the mule.