[Butch Cassidy Slept Here]

whether the animal would pose a direct threat to the health or safety of others, whether it would cause a significant disruption of cabin service

I won't say you could drive a Mack truck through this loophole, but definitely a large SUV. As to the matter of an uncrated goose: This passage seems to back-up the airline on all counts. The goose crapping on other passengers, or elsewhere in the cabin, is covered by the "health" clause. An unhappy goose will bite. So the "safety" clause applies. And a goose sitting in the aisle definitely blocks the food/drink trolley and interferes with the movement of the flight attendants (even though, in some cases, the goose probably has a better personality!) so the "cabin service" clause would apply.

For eight years I worked in an office campus which was innundated by geese. I swear those animals must live on ExLax. Walking to lunch was an obstacle course!

As to the responsibility for interpretation: My understanding of the Federal system is that, yes, the DOT interprets. However, if someone is unhappy with the DOT interpretation, the US Court of Appeals For The District of Columbia has original jurisdiction and thus can review the DOT determination.