"More like four-fifths-hearted (80%). Increasing to nineteen-twentieths-hearted, at the end of seven weeks (95%)," Sirius says.
"And you don't need to ask anybody to test you," Remus says, in support of what both Sirius and Severus have said. "It's possible to create the images on your own -- it's only with the interpretation that you'll need assistance with."
"What's involved is recording the... Well, different people call it different things. It's not the soul, as such, but let's call it the soul's biomarker, because observing it allows you to make inferences about the condition of the soul. What you see in the images -- that's the invasive part, because it reveals things about you, or about people close to you. But the number of images captured at any point in time, whether they're spread out or clustered together in a handful of places, and whether there are recurring patterns in the images over time -- these tell you something about how healthy the soul is, and whether you're carrying just your soul, or part of someone else's.
"And that takes time, because the biomarker is constantly changing all the time anyway. Or at least -- it is in a healthy person."