The shop did not sell unicorn blood, as the sale of it was forbidden. A large sign was posted on the shop's door warning patrons not to ask about it.
Behind the scenes
'Mulpepper' seems to be a reference to Nicholas Culpeper, an English botanist and pharmacologist who was accused of witchcraft after angering his fellow physicians by condemning their greed and their use of harmful practises such as toxic remedies and bloodletting. A revolutionary, Culpeper was able to provide his services for free. This, and a willingness to examine patients in person rather than simply examining their urine (in his opinion, "as much piss as the Thames might hold" did not help in diagnosis) created an affray between him and the Society of Apothecaries, who were similarly incensed by the fact that he suggested cheap herbal remedies as opposed to their expensive concoctions. Culpeper's Complete Herbal was one of the reference books that J. K. Rowling used when writing the series.
Despite standard British English punctuation rules dictating that a full stop does not follow a title such as Mr, Mr Mulpepper's Apothecary includes one, following the standard American convention instead.
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