Mice in the airplane.

I'm surprised to not see any mention of the most common rat/mouse trap
from when I was a kid.

It was a bucket about half full of water with a piece of newsprint or
masking paper drawn tight across the top. Using a RAZOR, or a knife
having a razor-sharp blade, the center of the paper was cut in an X-
pattern about half the diameter of the bucket. Suspended over the
bucket was the bait, usually a glob of peanut butter or a piece of
bacon rind. If suspended from the ceiling, a rat-guard was fabricated
from dead soft leading edge material.

In use, the rodent would go for the bait, the paper would refuse to
bear its weight and into the water it would go.

In a closed hangar the bucket was checked about every three days;
about once a week in an open hangar.

Zero cost. A chore that usually fell to the line-boy (me), who didn't
like to look when I poured the contents of the bucket down the
toilet... although we occasionally caught some GOOD SIZED rodents.

-Bob