Doorbell video shows one cat dragging the other down Hastings Road around 4 a.m. Wednesday.
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A neighbor actually called the police two hours earlier, after hearing the cats fighting.
Experts with The Department of Fish and Wildlife say the cat killed in this incident was a female, and believe the aggressor was a male.
"We don't know what motivated these lions to get into a fight, it's not extremely unusual, but it is unusual and it is noteworthy that it happened in a somewhat residential area," Ken Peglia said.
VIDEO: Mountain lion stares through window into Scotts Valley home
This is the latest mountain lion incident on the Peninsula, and Belmont specifically.
Last August, a lion was spotted walking across a driveway on Mezes Avenue -- a mile and a half from today's location.
And just last week, we reported a sighting in a Daly City backyard.