Some serial killers display one or more of what are known as the "MacDonald triad" of warning signs in childhood. These are:
* Fire starting, or arson invariably for the thrill of destroying things, for gaining attention, or for making the perpetrator feel more powerful.
* Cruelty to animals (related to "zoosadism"). Many children may be cruel to animals, such as pulling the legs off spiders, but future serial killers often kill larger animals, like dogs and cats, and frequently for their solitary enjoyment rather than to impress peers.
* Bed wetting beyond the age when children normally grow out of such behavior.