"The Rats in the Walls" by H.P. Lovecraft

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"Paris green" (Cu(C2H3O2)2·3Cu(AsO2)2) is a green pigment that historically was also used to kill rats and insects.

"Arras" is an obsolete term for tapestry.

The picture used is "The Rat Wants Out" by Don DeBold, used here under the Creative Commons Attribution 2.0 Generic license (https://creativecommons.org/licenses/by/2.0/)

To follow along: https://www.hplovecraft.com/writings/texts/fiction/rw.aspx

If you need some help, like I did, with some of the lines there near the end, I found this post here which certainly sounds like it could be right, and hopefully is. If you have knowledge of the languages in question, please drop a comment below with your input!

https://www.sffchronicles.com/threads/37245/page-2

"'Sblood, thou stinkard, I'll learn ye how to gust", could be something like "God's blood, you pig, I'll teach you to like the taste!"

"Wolde ye swynke me thilke wys?" means "Would you toil for me in such a manner?"

And for the final "Dia ad aghaidh 's ad aodann ... agus bas dunach ort! Dhonas 's dholas ort, agus leat-sa" (you'll have to pardon, I have no idea how to pronounce old Gaelic, I did my best with what I could find as a guide...)

"Dia ad aghaidh 's ad aodaun..." Aghaidh and aodaun (an old spelling for aodann) have the same meaning -- face, visage, or forehead -- so the oath is probably a standard one -- "God in thy face and thy visage!"

"... Augus bas dunach ort! ..." "... And death-woe on thee!"

Dholas (grief, desolation, abhorrence) and dhonas (mischief, misfortune, bad luck) are next wished on Norrys, followed by the leat-sa of which the -sa is an adjection of great emphasis -- perhaps rendered best as, "Grief and misfortune on thee, and with thee for ever and ever!" (pp. 149-151)

Or, in Fiona Macleod's (William Sharp's) own phrasing (taken from Best Psychic Stories, p. 146): "God against thee and in thy face ... and may a death of woe be yours ... Evil and sorrow to thee and thine!"