If you observe an iguana up close, you might notice a rather peculiar head wagging or bobbing. It doesn't mean you're dealing with a weirdo iguana. It means he's sending you a message -- perhaps even a territorial one that means "back off."
An iguana's head wagging can be an assertive behavior. It might be telling everyone around him that he's the boss and that they're on his turf, not the other way around. Essentially, it's an expression of dominance and territoriality. Physically mature, fully grown male iguanas are particularly partial to these wagging actions. However, female iguanas also do their share of territorial head bobbing. If you notice an iguana slightly elevating his bodily posture as he bobs his head, he's probably feeling pretty territorial at the moment.
An iguana might move his head around as a way of saying "Hello" to you or anyone else in his vicinity. If an iguana hasn't seen someone -- human being or reptile -- for some period, the head bobbing can be his subtle way of communicating, "Oh, how nice to see you. It's been a while."
Especially fast head wagging from side to side probably means the iguana is pretty irked and impatient. In some situations, it might even indicate that he's about to physically attack, so be careful.
If an iguana simply isn't the mood to be around anyone else, he might bob his head as a way of expressing that: "Go away. I don't feel like being around you at the moment, so try again later."
Bizarrely enough, head wagging often can be a sign that an iguana is showing off, plain and simple. If an iguana is feeling pretty good about himself, you might notice this jovial and spirited action, often followed by a classic up-and-down head bob. This motion sometimes is a way of getting the attention of nearby female iguanas.