All of them played by leopards who had been spiked with ket and then wedged into "spacesuits".
In some photos you can see the tails sticking out of the top of their trousers.
Sailers didn't think they'd fall off the edge, they could see that approaching ships and other features appear top first (e.g. the top of a mast before the rest of the ship) as they come over the horizon. So they knew it was round.
They're in on it too.
If we knew the moon landings didn't happen then we might start to question how Australia can be on the other side of the world when the world's flat.