We were at the Henry Vilas Zoo in Madison a couple of years ago...it's a free zoo, sort of small. Anyway, there was this polar bear and it was on a platform separated from the humans by a 6 or 8 foot trench...can't remember the exact size but it didn't look entirely adequate. And the bear was acting weird- it was pacing rapidly back and forth, looking at us, looking at the trench, pacing some more. It looked like my cats do when they're trying to decide if they can make a jump or not.
Operating strictly on instinct, I suggested we get out of there. And later I found out that there had been some sort of attack there sometime in the past.
Anyway, here's the bear.
I think humans really underestimate big animals. They're just not pets.