It's such a nice feeling when you see something that makes you suck the air in through your teeth and proclaim "COOL!".
If digital publishing was made for anything at all, then clearly it was for this book and the way it responds to you interacting with it. Each part of the HMTW (HMtW!?!) project is a lovely crafted jewel that looks like it will fit together with the others to make an arcane pocket-watch of uncanny beauty.
"We've caught a harpy, which bit do we make the potion with?".
"Not sure; which bit do you want to try first?"
"It's ...erm... ear?"
"On you go then, here's the alembic..."
"And you'll try another bit if it doesn't work?"
"Oh, yeah, definitely, I'll do that, yeah, no question, if it doesn't work... yeah..."