On the corncob issue:
If it's reasonably biodegradeable, such as corncobs, orange peels, pistachio shells, etc., proper etiquette would be to take 'em with with you, but as that isn't always practicable, it's okay to leave them if they're discreetly tucked away. Not flung into trees, you little hellion.
Anything else besides fruit and veggie leavings, and perhaps bread, is a no-no, and you will be punished with twenty lashes and be put in the stocks for two days.
It is revolting to come upon somebody else's foul little detritis. Makes me wanna puke.
On the squished bird/duck issue:
Mmmmm.........crispy aromatic duckling with hoisin sauce and pancakes. Deeeelicious.