riddle

One night two rats discovered a mirror, and noticed their reflections. They stared into the mirror for a long time and the first eventually disclaimed: “If we were our reflections, it would be amazing. Cats could not chase us, as we'd be too far away, hunters could not find us during the day as we'd be invisible, and we'd always be able to spy upon the dog to see it coming.” The other rat thought it a great idea, but to their dismay the plan was thwarted when they could not enter the mirror.

This activity managed to draw the attentions of a few birds, who had heard the conversation. One by one, they all looked into the mirror expecting to see something new. The owl, the crane, the herron, and the kite couldn't see anything that made sense. The tit chirped happily, seeing herself just as she was. To this they flew away.

Lastly, came the dog, who considered his reflection for a long time, then smiled a careful smile. He thought how lucky it was for the rats that they could not become their reflection, for they would be no match for the dog that had done the same.

What did the rats see?