Green’s Dictionary of Slang

snakes n.

[from the snakes one supposedly sees, i.e. see snakes under see v.]

[mid-19C+] alcoholic hallucinations, delirium tremens.

In phrases

have snakes in one’s boots (v.)

[mid-19C–1940s] to be suffering from delirium tremens; in weaker use, to be very drunk.

put snakes in someone’s boots (v.)

[late 19C] (Aus.) to disconcert.