[KholdStare]

I think. If you want more detail:

Spoiler for End of Season Two/Start of Season Three:

Aang went into Avatar state and was shot in the back by Azula's lightning. Sometimes when his back is bare you can see a red scar where it hits. Katara used the water she collected from the koi pond to heal Aang, but he was still stuck in the coma. However, she showed this water to Zuko, and while the Fire Nation thought that Aang is dead, Zuko alone knows that Katara can heal a fatal wound with this water. Zuko doesn't want to tell the Fire Nation that Aang is still alive because he just got accepted back into the kingdom. This is why he hired Sparky Sparky Boom Man to eliminate Aang secretly. That is where we're at.