The music actually has very little to do with snake-charming. The snake sees the moving flute and sways in sympathy.
Aizen doesn't talk about his past, not even to Gin, but Gin figures that there has to be something there. It goes beyond secretiveness, beyond even the caution that anyone like Aizen has to live by. It's a simple and absolute block; there's Aizen's smile and there's nothing else, and if Gin persists, he regrets it.
Gin knows he's not that much like Aizen. He's learned from the older man, sure, and he can fake it with the best of them, but Aizen can live the part in a way that Gin can't. It's as if Aizen can genuinely be the good captain that Gin knows, knows is all pretence. It's as if Aizen can honestly care about little Momo-chan while simultaneously working out how she's going to die. See, Gin knows his own pretty shell is lies, and he knows what he is underneath it, and that's one of his greatest strengths. Aizen isn't like that. Aizen is either lies all through or truth all through on both sides, over and under, and Gin's nothing like that.
But there's a similarity there, and when Gin first saw Aizen, something in him opened its eyes and hissed in recognition.
The snake charmer trains his creature before bringing it out in public. This may involve introducing the snake to a hard object, so that the snake learns that striking it causes pain.
Gin was a real quick learner. He always had been. As soon as he realised that he wasn't going to break Aizen-taichou's will or twist him round his little finger any time soon, he accepted the realities of the situation, sat down and studied, practiced, improved. He did everything that Aizen-taichou wanted. A sensible man can appreciate his situation, right? Better to accept his master than to beat his head and break his teeth against steel.
But perhaps there was a time or two, right at the beginning, when he tried to see what sort of reaction he could get out of Aizen-taichou, before he learned it was better to get reactions out of other people. Less painful for him.
But there was a time when he wanted to run poison in Aizen-taichou's veins, for so many reasons: because Aizen-taichou was starting to own him; because he was angry; because he was afraid; because he wanted to see Aizen-taichou weak. Because he wanted to.
Many snake charmers learn to read their animals and can tell if they are ready to strike.
Gin toys with thoughts; he knows that Aizen-taichou knows about them, he even thinks that Aizen-taichou would expect no less from him. They range from the simple to the complex to the murderous.
But each time that he comes near an edge, that he truly begins to entertain notions of striking . . . Aizen-taichou says something that turns the blade of his emotions, or that changes his line of thought, or that distracts him, or that gives him another target.
He has come to the conclusion that Aizen-taichou knows him far too well. The thought in itself pleases him. He knows that he dances to Aizen-taichou's orders. It's good to serve someone who knows you soul and blood and bone. For that he'll submit and obey.
For the moment, at least.