[There's another irritable snap and one of the vines tries to reach the umbrella to yank at it, but then his focus wanders back to Sherlock.]

When I left the room. We all changed when we left the room. ... Well, actually probably before then, it was kind of weird and super painful, our bodies were all wrong and squishy. At least I think. It was dark? But we were finished when we left the room.

And then I could do this.

[He moves the hand not currently occupied with vinehissing at Mycroft, spreading a handful of saplings and spores on the ground around them. They quickly take root, intertwining and creeping over the icy surface.]