"There are times when we perceive ravens to communicate with us. Craig Comstock, a raven-watcher from Starks, Maine, wrote of seeing a raven flying overhead. Craig called out, 'Hey, how's it going?' The raven immediately pulled a U-turn, did a half-roll, then went back on course. Craig waited until it had gone a bit farther and called again. Immediately, the raven pulled another U-turn, executed two back-flips and a half-roll before again returning to steady flapping. Craig commented, 'I can't prove the displays were for me. I understand the need for the scientific method, but...there are times when nature speaks just once, and it is a loss not to listen.'" --
Bernd Heinrich, in his authoritative and endlessly fascinating natural history of our smartest bird, Mind of the Raven.