Without looking at comments or anything beyond the first two lines: Lewis Carroll, Jabberwocky.

(I had to google for the title, though -- I recognised the poem but didn't remember its title. "Twas brillig slithy toves" as a search string found it quickly, though.)

FWIW, the very first word made me suspect which poem it was; the presence of "ag gírleáil 's ag gimleáil " in the second confirmed it.