Unsolved mystery: A bridge in Scotland where dogs commit suicide

The incidents were first recorded around the 1950's or 1960's when it was noticed that dogs - usually the long-nosed variety like Collies - would suddenly and unexpectedly leap off the bridge and fall fifty feet to their deaths.  

In some cases, however, the dogs would survive, recuperate, and then leap off the bridge again.  The locals have a name for these dogs: second-timers.