“What is up with your cat?”

I looked over at her. She was sitting on the floor, staring up at the ceiling. I looked closely at the ceiling myself but saw nothing there. So I turned back to my friend to offer the simple explanation. “Invisible mice.”

“What?”

“Invisible mice. I don’t know if you know very many cats. Sometimes they sit and stare for a long time. Sometimes they suddenly start racing around the house for no apparent reason. It’s because they see mice that we can’t. Invisible mice.”

“That’s not true.”

I shrugged. “It’s the best explanation I have.”

We went back to watching TV. After my friend left and I had turned off the television, I heard something. Faint scratching was coming from the ceiling where my cat was still staring. After a minute or so, it started to move. I followed it to the back of the house where a sliding glass door led on to the deck. Soon, a squirrel emerged from the side of the house and ran along the railing. Outside, I saw a hole where the wall met the eave. The “mouse” was no longer invisible. My cat had uncovered an intruder.

I knew I had to plug the hole, so I got a can of spray foam from the hardware store and filled in the hole. Problem solved. No more squirrel.

Or so I thought. The next day, my cat was watching the ceiling again. And sure enough, the scratching had returned. I went out to the deck to find bits of foam scattered everywhere. He had chewed his way back in.

Clearly, I needed a sturdier patch. I found a small piece of wood and wedged it into the hole. That seemed to effectively close it off, and I doubted that the squirrel could get past it.

I was right. But the squirrel had another trick. A few days later and more cat staring, I found that he had chewed a new hole directly into the eave. The only way he could have done it was to crawl along a wire leading into the house. There was no other place for him to sit and do the damage he had caused.

My cat was going nuts. She wanted to go out there and teach the squirrel a lesson. But she was an indoor cat, and I wasn’t about to let her out now. Still, I shared her frustration. The invisible mouse had become our white whale.

Putting up more wood didn’t seem a viable solution. After all, maybe he would chew through that, too. So I took a piece of a metal dryer vent hose and cut out a section larger than the new hole. I carefully nailed it onto the eave. There was no way the squirrel could chew through the metal.

The next day, I found my cat sitting by the back door. The squirrel was sitting on the railing of the deck. I opened the door and we could hear him chittering angrily at us. My cat meowed then hissed; the squirrel scampered to the fence at the edge of the yard. Satisfied, she sauntered away having successfully chased off another invisible mouse.