In an experiment to demonstrate that lizards are smarter than they seem, zoologist and reptile expert crocdoc trained a monitor lizard named Alex to wave at the entrance of the enclosure whenever he wanted to be let out, explaining each step taken to get Alex to his goal.
One day I saw him doing a small wave with his arm, anticipating the movement of offering me his arm to be let out. Again I encouraged this by rewarding his behavior by letting him out of the enclosure. This immediately and gradually shaped the behavior, so his waves got higher and higher until eventually he was doing a bit of a high-five. The best thing about this is that he can now get my attention more quickly than he would by just waiting on the side of the enclosure.