Apparently domestic Cats sometimes see us as incompetent kittens, who clearly can't actually catch rodents, birds etc ourselves, so they bring back live animals for us to chase around and capture, in much the same way as they would do with their own kittens.
Oddly enough, of course, many of the behaviours that in turn we do to them, petting, feeding etc, is us treating them like kittens, rather than adult cats.
