DUMBARTON, Scotland — “I was sure she was dead,” Lottie Mackinnon said quietly.

Ms. Mackinnon was sitting huddled in the corner of a cafe with her two children, sipping hot chocolate as she described the day three years ago when she was walking with her Border collie, Bonnie, over the Overtoun Bridge in Dumbarton, Scotland.

“Something overcame Bonnie as soon as we approached the bridge,” Ms. Mackinnon said. “At first she froze, but then she became possessed by a strange energy and ran and jumped right off the parapet.”

A bewitched dog lured to leap off a bridge by a malevolent force? It sounds like a preposterous scene straight from an old “Twilight Zone” episode.

But Ms. Mackinnon’s dog is one of hundreds that Scots insist have suddenly been compelled to throw themselves off the gothic stone structure since the 1950s. Many have ended up dead on the jagged rocks in the deep valley bed below.