would expect- just like Death, but instead of a human skeleton they possess that of a rodent. They appear alongside Death in multiple illustrations.
As an anthropomorphic personification, Death of Rats is able to project behaviour and emotion Death himself cannot. They mischievous and also escorts gerbils, hamsters and guinea pigs as well as rats. In Soul Music, Death of Rats also attended to the Head of the Musicians Guild, implying that being a rat in a metaphorical sense is close enough.
They often consort with a raven who acts as a translator, possibly one of Blind Io's before they were decommissioned.