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Venetia - Georgette Heyer

Yeah. So. Hunt the Squirrel. I overcame my trepidation and Googled it.

 

Hunting the Squirrel

 

An amusement practised by postboys and stage-coachmen, which consists in following a one-horse chaise, and driving it before them, passing close to it, so as to brush the wheel, and by other means terrifying any woman or person that may be in it. A man whose turn comes for him to drink, before he has emptied his former glass, is said to be hunted.

 

Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.

 

http://www.fromoldbooks.org/Grose-VulgarTongue/h/hunting-the-squirrel.html