Laura Thorn's clipboard

"Brilliant! Let's see… it mentions 'O2' and '50m'. A strange Muggle code? You're right, it's referring to oxygen and depth! This is a calculation for diving. Laura was planning a dip in the lake."

- Mathilda Grimblehawk

Muggle creature hunter Laura Thorn kept a clipboard in which she made diving calculations after hearing that the landlord of the Siren's Rest, in Wales, had been attacked by some sort of creature in the nearby lake.

Ministry of Magic investigators Mathilda Grimblehawk and her partner later found this clipboard in a lakeside grotto and, after magically clearing the water damage, read it just to realise that the Muggle probably planned to dive into the lake, at the risk of being attacked by the creature.