Some airlines require you to display proof of onward travel before allowing you to board a flight to certain countries. The proof they usually require is an itinerary for another flight.
One of the dogs here is a rescue. His previous owners had him debarked. He’s a big dog and would have had a big bark. He still tries to bark now, but all that comes out is a hoarse whisper and bad breath. I don’t think he realizes that he’s lost that canine essence. I’m not sure he knows anything’s amiss. Easy to pity such a creature, but it’s not just dogs that get debarked.