J.K. Rowling wasn’t sitting in her study, impatiently writing and crossing out names for the Hogwarts houses. No — the famed “Harry Potter” author had to get creative when inspiration struck.

In a thread started by author Ruth Ware on Twitter, one fan said she was forced to write a thought down on a napkin because she didn’t have a notebook with her, which is why she always carries one with her now.

In response, Rowling said, “The best thing I ever wrote on was an aeroplane sick bag. Came up with the Hogwarts houses on it.”

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Had the houses of Hufflepuff, Ravenclaw, Slytherin and Gryffindor been named differently if Rowling had racked her brain for them someplace else? We just can’t imagine Harry Potter living in another house. Or Slytherin not being the house no one wants to be a part of.

Rowling has famously said that she first had the idea for Harry Potter while delayed on a train traveling from Manchester to London King’s Cross in 1990.

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Over the next five years, she wrote mostly in longhand and amassed a mountain of notes, many of which were on scraps of paper (and a sick bag, we now know).

Rowling most recently served as a writer and producer on the Harry Potter prequel, “Fantastic Beasts and Where to Find Them.” She will have the same credits on its sequel, “Fantastic Beasts: The Crimes of Grindelwald,” when it hits theaters next year.

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See Rowling’s tweet below.

The best thing I ever wrote on was an aeroplane sick bag. Came up with the Hogwarts houses on it. https://t.co/Fut4BvS6iM — J.K. Rowling (@jk_rowling) December 15, 2017