The ig likely perceives the iguana as a predator. It will extend its dewlap to make it look larger, bend its body and tail whack.. and a bite will occur if the threat is large enough. I have seen people posting pics of iguana bites quite a few times, to themselves, other iguanas, other pets etc. I cant remember who it was but someones pitt bull took a nasty little bite some time ago. I do not think the dog was asking for a fight though.