Pronounced Choy-yah, its name comes from the Spanish word for head. Personally I don't really see that much of a head like look to most of the plants. This type of cactus is just plain evil. It can reproduce vegetatively. That is to say any of the branches that comes off and touches the soil can grow a new plant, and they do often drop branches.
The jumping cholla (Opuntia Bigelovii) will often drop branches the moment a person or animal brushes against one. The needle like spines will then often work their way into flesh, clothing, or leather. Not in an extreme way, but I have more than once been cursing the darn things while pulling bits of them from my jean cuffs using leather gloves.
I avoid even getting near the cacti of genus Opuntia whenever I can. Which is not often when on trips to the desert southwest of the United States. They grow nearly everywhere from Four Corners down through the Mojave Desert in California. The barbed hooks make the spines an effective defense against most animals, except the kangaroo rat. They protect their nests with piles of the fallen joints.
To be fair not all are as noxious as the teddybear (what an ironic name!) or jumping cholla, but dang. None of them are particularly easy to get along with. Not that any cactus is huggable, but most don't seem so purposefully malicious.