I think he refers to having a system that, using this approach, turns on his shower when he enters it. If this cannot distinguish humans from cats, it would turn on the shower when a cat entered it.
I think that's a bad example. The typical cat would soon learn not to enter the shower.
If the system has enough lag, clever cats might dart in and out before the shower sprayed for a brief bit, so as to get some fresh water (which they like more).
I think that's a bad example. The typical cat would soon learn not to enter the shower.