Terrifying device for a field mouse

RATTRAP

A snapping contraption that turns a rodent’s last meal into its final mistake.

This clue plays on the literal meaning of "rat trap," a device designed to catch rodents, but frames it humorously as something terrifying for a field mouse. The word "terrifying" hints at the danger the device poses, while "field mouse" is a more poetic way to say "rat" in this context. The answer is straightforward once you realize "rat trap" is a single word when combined—RATTRAP.