Detective Cerveau led his colleague directly to the mirror. "Mr. Bete, I think we'll find upon closer inspection
that this mirror has the missing palladium in it." Upon saying this, he flipped the mirror over and rubbed his
hand over it, which developed a rash after a few minutes. "Mr. Vole, you're under arrest for the theft of this
palladium."

Information behind this:
In addition to being a slight skin irritant, palladium, when put behind glass, will form a mirror.