I won't actually end the world, silly ;)
I only create a highly infectious virus that activates certain parts of the human DNA still left over to form a tail and also inject some data into the cells that ultimately causes spread of the virus and planned mutation [UwO]
Walking moves the tail a little tbh.
There actually once was a robotic tail that was sold from an east Asian country. Many were sold. They were mass-marketed.
Yes I would like to become an actual anthro-animal.
But how would we go by that?
I mean...
We have sex-change processes.
Why can't we have species-change processes?
Likely because of genomes.
It is impossible to create a new genome or a brand new species.
At least with current knowledge.
But like you said, pathogens.
Something to take over our body and give us fur and animal appendages.
Even just temporarily.