Few mothers are fiercer than mother grizzly bears. They have to be, because their cubs are adorably helpless for most of their early development. Part of the wonder of watching mother bears with their cubs is their seemingly infinite patience, willingness to teach, and, finally, the astonishing speed in which they go from ambling along curiously to quarter-ton missiles of sheer, bowel-tightening rage.
The people who shot this video declined to say where it was shot, but it sure looks like it could be Montana or northern Wyoming to us. The people filming sound like a family, but they could also be a group on a wilderness tour. Regardless, they're alternately delighted and awed when they witness what follows.
The mama grizzly, considerably uphill from her cub, is rooting around the brush when a small coyote approaches her cub. The cub is unaware of the coyote's presence at first, but when it becomes aware, it jumps in surprise, which the mother hears. All at once, she's tearing down the hill towards the coyote with an audible growl.
The coyote gets out of her way with all expediency, but the human witnesses are, you might say, shook. Finally, the bear notices them, at which point they wisely think it prudent to take their cue from the coyote.