A couple from Montana were out riding on the range, he with his rifle and she (fortunately) with her camera.  Their dogs always followed them, but on this occasion a mountain lion decided that he wanted to stalk the dogs (you'll see the dogs in the background watching). 
Very, very bad decision.  The hunter got off the mule with his rifle and decided to shoot in the air to scare away the lion, but before he could get off a shot, the lion charged in and decided he wanted a piece of those dogs.  With that, the mule took off and decided he wanted a piece of that lion.  That's when all hell broke loose.

As the lion approached the dogs the mule snatched him up by the tail and started whirling him around, banging its head on the ground on every pass.

He dropped him, stomped on him and held him to the ground by the throat. The mule got down on his knees and bit the thing all over a couple of dozen times to make sure it was dead, whipped it into the air again, then walked back over to the couple (that were stunned in silence) and stood there ready to continue his ride...as if nothing 
had just happened.

Fortunately, even though the hunter didn't get off a shot, his wife got off these 4.

Photos from
http://www.lablaughs.com/adult_toon.php?id=A19930210

http://www.lablaughs.com/adult_toon.php?id=A19930211

http://www.lablaughs.com/adult_toon.php?id=A19930212

http://www.lablaughs.com/adult_toon.php?id=A19930213
. .

. .
. . . .
. .

. .
. . .
Snopes.com describes this story as real pictures, but inaccurate description at http://www.snopes.com/photos/animals/mulelion.asp