I had something interesting happen to me on a transcon last week... A pax walked down the aisle leading a very large dog on a leash. It did not have the harness/vest that I have seen on seeing eye dogs, so I'm thinking it was either an anxiety therapy or seizure dog.

I was sitting in C, so I didn't get a chance to see the logistics involved, but does the dog get its own seat? I didn't hear any commotion or barking or anything, so I'm sure it was very well behaved. Just something interesting I had never seen before.