If you look up the definition for an Object, it specifies that it is “a nonliving, distinct thing” — such as a corpse.

However, the definition of Creature does not say it must be living. So, a corpse is both a creature and an object.

There are even creatures that have never been living — such as constructs — and thus are also objects.

There is some gray area as to when a corpse is a corpse or just mostly dead. They aren’t an object until they are all dead.