Potato flakes can indeed kill mice. Instant potato flakes can be placed out for mice. Once they consume the flakes, they become very thirsty. ... This causes those flakes to swell up inside the mouse's stomach, and this will kill it.

Will mice eat potato flakes?

Instant Mashed Potato Flakes– place instant mashed potato flakes on a shallow lid and place in areas where signs of mice have been found. Once they consume it they will seek out water, causing the flakes to swell in their stomachs, killing them.

Will mashed potato flakes kill rats?

"KILLER MASHED POTATOES":

Other natural remedies include what Bader calls "Killer Mashed Potatoes." Leave a bowl of potato flakes and a small bowl of water out. Rats that eat the flakes and drink the water will be killed when the flakes expand in their stomachs, he said.