So, an “eternity box” is a coffin, to “hop the twig” is to run away & “balderdash” is adulterated wine. Enliven your vocabulary with this & much more 18th century slang, as recorded in Grose‘s Classical Dictionary of the Vulgar Tongue (1788):
Etymology of Phrases —> “As mad as a hatter”
In the 17th and 18th centuries, hat-makers (hatters) often had cognitive issues (or went mad) as a result of mercury poisoning, a side-effect of manufacturing felt hats. The famous Mad Hatter of Alice in Wonderland is also a play on this phenomenon.