This letter grid for mirror-flashed code (from The Girl of Ghost Mountain by Joseph Allan Dunn, 1921) can serve as a Boggle puzzle.

We found several five-letter words relating to: an obstinate person; a collector of dirty water; a swelling protuberance; a portable illumination; another word for "cusk"; a second growth of hay in one season; a monetary unit replaced by the forint; and a plate for consecrated bread.

Here are all 18 words we think are contained within the grid (including archaic ones).  Highlight the black to reveal the text: bigly, bigot, bilge, bilgy, bulge, bulgy, glims, gowks, newly, oaten, paten, pengo, rowen, torch, torsk, works, wrote, zorch