CHICAGO -- The horse reared and struggled as if fighting an invisible assailant.
Chicago Officer Paul Casasanto, on mounted patrol at North Avenue beach, had slid off the horse as it began to struggle inexplicably.
"Mik just went down," Casasanto said in to a police radio while holding tightly to the horse's reins.
Casasanto tried to calm his horse while people in bathing suits and jogging clothes began closing in.
"Stay back," he warned, as the animal continued to kick its powerful back legs.
After several weakening attempts to stand, the horse folded to the ground and rolled onto its side.