On the trail, in the dressage arena, at the racetrack, on the cross-country train–wherever horses may be, we've all seen it: the "Spook"–that sudden, bolting reaction of shock so particular to our equine friends. It might be because some animal runs up, or some object is blown in by the wind, taking the horse by surprise. But sometimes it's just something you're sure they've seen many times before–so why spook about it now? New research at the Aptos, California-based Equine Research Foundation (ERF) now has answers to that question.

According to Evelyn B. Hanggi, MS, PhD, co-director of the ERF, one theory about spooking is that objects appear different to horses when viewed from various angles. Hence, a mailbox, a sign, or a pile of bars could take on new characteristics when viewed from another side. "What we wanted to know was whether the horses could understand that the parts equal the whole," she said.

Hanggi believed they could. "If not, they would spend much of their time spooking and running away from everything," she said.

To test her theory, she established an experiment in which horses were trained through positive reinforcement to select one of two toys: a lizard rather than a dinosaur; a mower instead of a wheelbarrow; and a tractor instead of a truck. Initially these objects were always placed in the same position. But once the horses were well-trained, Hanggi started rotating the objects to see if they could still identify the "correct" choice. Positions included backward, sideways, and upside-down