The Space Between Failing and Falling • Snarry •

Chapter 4: Restlessness Before Reprieve

He sits by the fire in a black mood. By the time there's a knock at the door, he has already drunk most of a bottle of red wine.

It's midnight.

He opens the door, and no one is there.

Then, the messy head of Potter appears from under that blasted cloak. Like the quintessential Gryffindor he is, he barrels in with nary a concern to the consequences.

"You never think—" Severus does not know what he is saying. He has the wherewithal to check that his grandmother's portrait curtains are closed.

"Um...I'm sorry to just b-barge in but..."

On closer inspection, he can see that Potter is close to tears.

"You should not be in here," Severus says. "Your Head of House would be more appropriate—"

"She...wasn't there." He hugs his arms. "She wouldn't understand."

"I wasn't there. I was in St Mungo's. Thanks to you."

He receives a dirty look. He deserves it.

Potter flumps into an armchair beside the fireplace and wraps his arms around his legs. "Sometimes I think if I didn't love anyone...then I wouldn't have anything to lose." This remark, coming from Potter's lips of all people, is untenable. He mumbles into his knees, "I can't sleep. Talk potions to me or something."

"I am not your Potions master."

They both know that this is a feeble excuse. Severus sits on the sofa and tops up his wine glass.

Fuck it.

"The magical signatures arising from several analytical brews, and logical fallacies to consider before one starts on isolating the components," he begins.

Harry snuggles into the wing of his chair and shuts his eyes.

"Firstly, the differences may contain more than one component, element or technique. It is vital that one understands a result can arise from two or more components."

He knows that he is over pronouncing his consonants, and grips his glass harder so he isn't tempted to wave his hands as he speaks.

"The second limitation is that it is susceptible to the synergies between the variable of interest and the factor that is varied to create the difference. Fortunately, when two factors influence the same component, they are likely to interact multiplicatively.

"For example, the amplitude of the effect may be twenty percent greater for one ingredient over the other, leading to a larger absolute difference in the amplitude of the signature."

His voice quietens as he watches the boy's face relax.

"Of course, the interactions could take a more complex form that would lead to unexpected results. This could be particularly regrettable if one were experimenting with especially volatile substrates. We work on the theoretical premise that one has taken steps to reduce the magical noise within the environment. It is a big assumption indeed, to assume that there are no magical instruments in the vicinity, no self-cleaning cauldrons, and no house-elves. Of course, that is why it is best to be in an underground laboratory when deconstructing such potions."

Potter's glasses are slipping off his nose.

"It also bears mentioning that the signal-to-noise ratio of a difference in effect will be lower than the original comparisons. Specifically, if the original signatures have similar noise levels, then the noise in the difference wave will be greater by a factor of the square root of two—so, approximately forty percent larger..."