Siri, especially, seems to love this kind of rough play. She will try to get Brea to chase her, by play-bowing in front of her, poking her with her nose, or running into her at high speed, until Brea stops what she's doing and goes after her. It looks pretty alarming, but Siri actually seems to like it when Brea knocks her down and grabs her by the collar. Sometimes it looks like Siri lets Brea catch her. Often, if Brea loses interest, Siri will start the process all over again. The only real drawback that I've seen is that it's kind of hard on Siri's collars.