My great-grandfather had a big ol' mule named "Bessie" who was the meanest thing on earth. He could work with her but heaven protect anyone else that came near her. She'd as soon bite or kick you as look at you. I wouldn't even go into the barn when she was in her stall. Scared me to death.
A mule is a cross between a horse and donkey. However, it's a cross between a mare (a female horse) and a jack (a male donkey, thus the name jackass). Apparently, it's pretty rare for a male horse and female donkey (called a jenny, BTW) to hook up and produce offspring. But when it does happen, the result is called hinny. And offspring of either pairing are almost always sterile.
I remember that day well, Cory told his brother Brandon [ who was on the donkey with him], 'she'll bite you', Brandon. Then Brandon was sneaking something in the car and Cory said, "thats not yours Brandon, put it back". He was always so smart. She would bluff the kids but never bite or hurt them.
The park I walk in is surrounded by mountains. When the weather is warm, there are lots of snakes. Here's a friendly one I took with me on my walk. He was climbing into the playground, scaring people who didn't know he was non venomous: