When Orochimaru learns her first jitsu, it feels like finally, finally, this world has opened up with possibilities. The henge jutsu: you truly become the form you take.
The only real draw back to this is the more radical the change and the longer it's held, the more exorbitant the chakra cost. So, turning into something like, say, air or mist, for even just a few minutes means complete chakra depletion for anyone below, say, a Jōnin. And then senses can be muddled or muted or even negated depending on what you turn into.
So, there were some finely drawn limits, but otherwise? A priceless jutsu, especially because it wasn't an illusion.
It takes her only days to break down the process and refine it to an art form, or rather, one form in particular.
(Orochimaru becomes the person she used to be for twenty-four seconds, but those twenty-four seconds are precious and make everything feel right for once, like a missing piece sliding into place.
For twenty-four seconds, Orochimaru is completely at peace.)
Orochimaru practices the henge multiple times a day and near constantly while in school. She tests the limits. Henging parts of her body like a hand or part of her legs and her clothes, making them something different entirely and trying to hold it as long as she can while dividing her attention with the lectures. Other times, she only makes a very tiny change that's almost unnoticeable, like the texture of her hair or ever so slightly darkening her skin tone so it looks more human, more like a pale ivory instead of a deathly pallor.
The instructors notice (how could they not?), but say nothing, giving only approving looks on occasion and mentioning among themselves a rising young Kunoichi who might just graduate within a year, the youngest yet, a once-in-a-generation genius. There were mutterings that if Tobirama wasn't so busy, he might take one last student. However, with the war brewing on the horizon, one of his three students might take the position of sensei instead, as it was about time for them to do so.
Orochimaru isn't deaf, nor is she oblivious, but she can't help but be worried over how they will react to her failing the graduation exam, as much as she can realistically get away with.
It doesn't bode well in her mind.