Except they spit.
It's how they express themselves.
For 10 feet around any iguana roost, you'll see little off-white blobs everywhere. And if that happens to be in the front window of your groovy San Francisco apartment, where the iguana sits in the window all day and spits at passers-by... it gets pretty damn disgusting.
(Not that I have traumatic personal experiences with a friend who had iguanas. In San Francisco. No problem at all. Blech.)