What is the big red thing under a lizards mouth/head?

I've only seen it come out once but he was bobbing back and forth too. He wasn't mating because he was by himself.
Hey well first of all id keep away from it lol. usually lizards that have a dewlap expand it when they feel frightened or during mating season and looking for a mate. The head bobbing is a dominance characteristic! if you have more than two lizards, one will bob their head showing their dominance, in most cases males. HOpe i helped. take care!
It's a "dewlap" (I'm guessing you have a Green Anole?). They also use them in territorial displays.
It is called a dewlap. It is most likely a Green Anole. He thinks you are intruding on his territory! Thats kind of funny. They only get 4-8 inches long (including their tail) They can bite but it doesn't hurt. They are pretty common for people to have them as pets if they are just beginning with reptiles. Why do you want to know? Do you want to keep him? or are you just frightened or curious or something? http://en.wikipedia.org/wiki/green_anole... They can also change colors to brown if they are uncomfortable.
Hello ...Kudos on just watching ..not trying to catch it..it's called a DEW-FLAP..many lizards have them including iguana's they display them when stressed, showing their territory or during breeding seasons ...Take Care :)

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