A week or more ago, Bela had somehow cast off his collar; it lay next to the front door. When the dogs come in at night - which they always do, for an hour or two at least - Charlie goes to bed almost immediately, presumably half out of agedness/laziness and half out of the desire to find a surveillance/control point in the room. Barry however has a different mode of asserting himself - he trots around and finds things to do, minor annoyances so we tell him off and his existence and importance is reaffirmed. Last night, he found Bela's collar and took it into his bed to chew (it tasted like a cat's neck, presumably).
The ringing of the collar bell immediately got Charlie awake and aware. As far as Charlie was concerned, there was some cat, its bell resonant, just flagrantly and actively present in the room. Barry, unaware of the effect on Charlie (he was facing the opposite direction), continued to harass the bell. Charlie was bolt upright trying to pinpoint the location of what was clearly, to her, a prancing and audacious cat. She got up and went to every possible corner of the room, at each point listening again for the bell, which was persistent but less revealing each time. Finally Barry cottoned on that Charlie was excited about something strange in the room, and both went into sentry mode. They patrolled for some time until Barry got sick of the lack of hard evidence and went back to the collar. At which point Charlie started all over again.
It could have escalated and been even better slapstick but then Barry got sick of what was, surely, a pretty lame chewing exercise and went to sleep. The end. But a good scriptwriter could spin that into something pretty fine I would say.