thats his dewlap. it puffs out like that (its flat) when they "talk" or "threaten" . it makes them 'seem bigger' to other animals. which is why you see yoshi running away.. hahahahaha. If you go on youtube.com i have video's of chomper you can look at if you would like to . just type in chomper the iguana. i cant access youtube at work so i cant send the links.
LOL!!!! I had a baby iguana before i got frankie, he was about 3 inches long... and i was scared of him because he kept whipping his tail, hissing and threatening to bite me so i exchanged him for Frankie who i am not scared of.
I have a phobia of fish... but those are kinda cute but i don't like there eyes, they freak me out. I think in a previous life i was maybe eaten by a shark or something, honestly i am more scared of fish than i am spiders!