[ It's interesting to hear her explain it, and it shows with the shift in his expression, because it's honestly something else that's a bit beyond his time, though he's learning the more he talks to people in the CDC, naturally. Germ theory wasn't exactly new, but it was still in its fumbling, careful stages in the England he and Ciel lived in, and for a creature that doesn't even fall ill at all, it's especially fascinating in its foreignness. ]

I can only guess at how difficult that may be. It is a bit hard for me to wrap my mind around at all, in truth...

[ He turns his attention back to the tree with a furrowed, thoughtful brow, since he's parsing through it and applying this new knowledge to what he knows of the world. ]

It is especially difficult for me, admittedly... To grow ill at all is an experience I have never had.