The Covid-19 Variants Of Concern that have emerged in recent months aren't just more transmissible or somewhat more deadly, they also possess new capabilities to infect other species beyond humans.
The British variant classic appears to have evolved to be more likely to infect pets. This can causes heart inflammation issues in companion animals.
Whilst the animals became severely ill, there wasn't any apparent effect upon the respiratory system, meaning that infection can be 'silent' and appear as a non-respiratory issue.
Meanwhile, the South African and Brazilian variants appear to have now evolved to be able to infect mice for the first time, albeit it doesn't appear to cause mice significant harm.
https://www.biorxiv.org/content/10.1101/2021.03.18.436013v1
Together, these variants may make herd immunity in humans more difficult, and provide opportunities for serial passage across multiple species especially as mice are low in the food chain.
Such zoonotic processes in labs are a key component in gain of function research. Therefore a 'natural experiment' in serial passage may similarly increase the rate of mutation, with the associated risk of newer strains evolving further capabilities.
I wouldn't be surprised if there is undetected transmission between various companion animals 'sniffing butts' and nibbling from each others dishes, and human lockdowns would seem to create a selection pressure to jump between more dynamic carriers.