Holmes has gone to the kitchen to prepare tea. He can readily hear what the others are saying and puts things on the tray rather harder than necessary. He comes back with the tea things. "To muddy the waters is par for the course. The problem is carefully tracing the source." He pours an over-generous portion of brandy in his tea. "Such potions you speak of can't be the norm. Is there anyone else save yourself who can form?" He waits, but apparently that's all. He takes a large drink of brandy-tea and reaches for pen and paper again.
"There are such things available to mundanes as well. Not spells naturally, but other methods," he writes. "Actually, if something of that nature happens, it will be a valuable clue in and of itself, for it will tell us that there is indeed something rotten in the state of Denmark."