Actor Ron Howard played the lovable young Opie on the show and there is a secret about Howard in the opening credits that few people knew. At the time of filming the opening credits, Howard was only six years old and was not strong enough to throw the stone far into the lake.
Producers decided to hide a prop man behind a bush and have Howard pretend to throw a rock. The prop man would then throw a rock into the lake, making it look like Howard had done it. If you watch closely, you can notice a lag between Opie’s throw and the splash in the lake.