What exactly is Combustionman's Tattoo?

Question

When the guy with the Metal Arm and Leg AKA Sparky Sparky Boom Man or Combustionman firebends we see something shoot out from his forehead when he's tattoo is.

during the episode The Runaway when Team Avatar is escaping Toph throws a boulder at him which he destroys but a fragment of it hits his tattoo causing him pain and when he goes to shoot again it seems to miss-fire. Sokka also seems to comment that he is firebending with his mind.

So i am wondering what exactly is Combustionman's Tatto because it seems to be the source of his bending but no other Bender uses a tattoo to allow bending beyond their arms and legs (like Boomi using his face of Toph tilting her head to fix a game)

Answer 1

This is semi-good source for Combustion Man. This is a good source for special bending techniques in general.

It states that his tattoo is a focal point for him to trigger explosions by focusing his chi. Seeing as it's a unique use of bending, I wouldn't be surprised if he can only bend from that spot simply due to complexity and a necessity for accuracy.

Additionally, the idea of the "third eye" is taken from Hindu tradition. THe combustion bending tattoo's is located over this Chakra, with the tattoo being of the Eye of Shiva. P'Li's is a more wavy version, which may be related to her ability to bend the beam as well.

All the bending are generally related to some kind of martial art, so if that doesn't answer your question, I'd be glad to do some additional research. Let me know!

Also, thanks to Ryan for the comment. It prompted the extra link and the tattoo design section.