Necking, also called playfighting or sparring, is observed on a regular basis among young adult male giraffes. In this ritualized practice, males take turns hitting one another with their massive necks and heads. Injuries rarely result from these exchanges.
Here, the older dominate giraffe appears to be teaching the younger giraffe the proper techniques of "necking". Or, it could be asserting its dominate rank.
This interaction lasted for about an hour.