One time when Ferdinand was about 8 months old (we had just gotten him), he was exploring his brand new cage. He had been living in a 5 gallon bucket before we adopted him, so I'm not sure how long it had been since he had sticks and vines to climb. He was going full force all excited, reached up, grabbed what he thought was a branch, and abandoned Chameleon Climbing 101 (three points of contact at all times!). Well... It was his horn not a branch, and he totally took a header to the floor!
He was fine, and after my heart attack stopped, we laughed ourselves stupid.