Large animals are especially dangerous when they are surprised or frightened. Domestic animals are no safer than wild ones: the bull is generally considered the most dangerous of domestic animals. Milder animals may inadvertently cause dangerous situations by, for example, straying onto roads. Animals trained to guard property pose a threat to those whose work obliges them to enter private property; even household pets can be dangerous if excited or frightened.
Smaller animals are equally dangerous. Parasites include insects, ticks, worms and protozoa. Snakes, spiders, scorpions, and lizards are often deadly, as are centipedes, insects, and some fish.