Any mad scientist - and by that, I mean any OTHER mad scientist - will tell you that it's not enough to cackle and prance insanely around the lab. Some lab assistants just don't get the hint.
So when going "Muahaha!" doesn't cut it; when Igor (or Igette) simply won't leave you alone with your mastodon/cuttlefish hybrid, your Dissolvo Ray, or your mind-melting Pscho-Cyclotron, just state the obvious.
