How did the plover learn it is safe to fly into crocodile's mouth?

That has been accepted since the time of Herodotus, who first reported it. I have never seen it nor seen  photographic evidence that it happens. Have you?

I'm not saying that it doesn't happen. Crocs gape while they bask to cool off, so a bird might be attracted to a bit of food inside the croc's mouth. But you'd think that someone would have photographed the action, wouldn't you?

His buddy double-dog-dared him to stand on the croc's tongue one night when they had been drinking heavily.