Dewlap

 Male anole's have a dewlap ( a flap of skin on the underside of the neck ) that they can be contracted or extended using a special cartilage.  Being almost nonvocal male anoles communicate via this dewlap.  When angry, it flashes its dewlap repeatedly and at the same time does push-ups to make itself look bigger and more intimidating.  A male also does this to impress the lady anoles. 

A few images of a brown anole with the dewlap in various stages of extension.  Notice the color shifts as well.