A small German study has found[1] cats are not likely a transmission vector (no transmissible viruses found on cats in households with multiple COVID-19 infected people.)

[1] https://www.zuercher-presse.com/virologe-hendrick-streeck-gi...

Most people let their cats out at night, then they socialize with other cats, and when they come home in the morning they carry the virus. And the humans socialize with the cats.

Then there are also other animals like small mice that now when it gets warmer outside move out and socialize.