But you can easily hear the crinkling noises they make as they scurry around the bag. Anything, up to and including shredding the bag, can be done to kill them. The arms of their easy chairs are great places to scratch and claw the fabric. You need to leave your mark on the world. This always gets their attention.
Hassocks are also good scratching posts.
It is advised that cats use any scratching post the humans may provide. They are very protective of what they think is their property and will object strongly if they catch you sharpening your claws on it. It is important to maintain one's Dignity when around humans so that they will not forget who is the master of the house. Humans need to know basic rules. They can be taught if you start early and are consistent.