Green’s Dictionary of Slang

flay the fox v.

to vomit.

1653		Urquhart (trans.) Gargantua and Pantagruel (1927) I Bk II 334: Which made all these good people there to lay up their gorges, and vomit what was upon their stomachs before all the world, as if they had flayed the fox.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Flay or flea the fox, to vomit.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1859		Matsell Vocabulum 33: flay To vomit.
1873		Sl. Dict.