A horse died and its owner fell unconscious within seconds of falling into decomposing green seaweed along the northern coast of Brittany, France, last week.

Vincent Petit, DVM, PhD, said he was hand-leading his 15-year-old English Thoroughbred gelding along a beachside road after riding a long stretch of gallop when both he and the horse slipped into an algae-filled sludge nearly up to the horse's withers.

"I cried for a man on a tractor to throw a rope, and then I looked at my horse and saw that his nose was falling into the sludge," Petit said. "I held his head up for him, but a few seconds later he went into respiratory arrest, without even a fight. It was incredibly fast."

Petit said that he became unconscious immediately after that and did not recover until he had been moved out of the sludge by passersby who prevented him from drowning after he lost consciousness