The Raven (Corvus Corax)details

There is a peculiarity belonging to ravens tht must draw the attention even of the most incurious—they spend all their leisure time in striking and cuffing each other on the wing in a kind of playful skirmish; and, when they move from one place to another, frequently turn on their backs with a loud croak, and seem to be falling ot the ground. When this odd gesture betides them, they are scratching themselves with one foot, and thus lose the centre of gravity. (p. 233)