There are certain subjects that are not appropriate objects of doubt. For example, I don't think it makes a lot of sense to doubt one's own existence: if you don't exists, what's doing the doubting?
If I may wax philosophical about large jungle cats for a moment:
Here's a quote from MSNBC's article about the recent tiger escape/attack at the San Francisco Zoo:
Experts doubt tiger could have leapt
One zoo official insisted the tiger did not get out through an open door and must have climbed or leaped out. But Jack Hanna, former director of the Columbus Zoo, said such a leap would be an unbelievable feat and “virtually impossible.”
Instead, he speculated that visitors could have been fooling around and might have taunted the animal and perhaps even helped it get out by, say, putting a board in the moat.
Ron Magill, a spokesman at the Miami Metro Zoo, said it was unlikely a zoo tiger could make such a leap, even with a running start.
“Captive tigers aren’t nearly in the kind of shape that wild tigers have to be in to survive,” he said. He said taunting can definitely make an animal more aggressive, but “whether it makes it more likely to get out of an exhibit is purely speculative.”
See, if your zoo finishes building its tiger enclosure and you take a look at it and there's doubt around the issue of whether or not it will, in fact, adequately contain the tiger, you know what: go back and redesign the tiger enclosure. Not an appropriate subject for doubt, zookeepers.