Well why not just ask? Technically they are the same person... Only different is Toxics was dog DNA and Tox was Fox DNA. Also there bandanas wore manufactured by different people after the big effect of the virus. Idk just a little thing nobody seems to think of... Where does the bandanna come from?
I mean it makes sense, they're different species.
I might be wrong, but maybe it implies that there was an experiment with toxic waste, or something happened and toxic waste spilled somewhere? Idk just theorizing.