The Mii'Ari, if you disregard various details, are basically an advanced species of genetically uplifted animals, that is animals who have been given an upright humanoid form and intelligence through some form of genetic engineering. The exact method by which they were uplfited remains something of a mystery, in that nobody can figure out whether it was a part of a survival strategy by another ancient species, an accident that occured due to that strategy, or just a massive genome manipulation experiment by the Doleans. The latter one is, understandably, rather popular with the people, and it's not helped by the fact that Doleans remain secretive on the matter, though it's clear they possess
some kind of relevant information. The existence of the H'Raghaurg, a somewhat similarly uplifted
canine species, also lends some credence to the theory, as the Doleans were the first to make contact with either of these races.
In any case, the uplifting agent, a symbiotic nanobiomechanical bacteria, had transformed the various felinoid life of the Mii'Ari homeworld into one of the most quirky intelligent races the Doleans claim to have met across the galaxy.
While it can't be said for certain what was the symbiotic agent's original purpose, in the end its integration with the Mii'Ari body became astounding. The nanobacteria had taken on almost all the body fuctions normally carried out by the body's own cellular systems. Comparisons to other, non-affected life on the planet, reveal that the internal organ structure of the Mii'Ari underwent dramatic alterations - in fact, beyond the basic nervous, respiration and circulation systems, nearly everything has been replaced in full. (uh, there's a lot of info I could dump here, but I suppose I'll just stop at saying "it's hella different", before I start talking about anatomical compatibility and reproduction cycles
)
The practical upshot of the above is that Mii'Ari are not only more agile and stronger for their size than humans are, they are also surprisingly hard to kill. The nanosymbionts repair tissue damage, conserve oxygen for later use, process any and all kinds of ingested material on a molecular level, and can actually prevent a separated, but otherwise intact head/brain from dying for up to several hours, by shutting off all blood vessels leading to the brain and creating an enclosed circulation system where the brain is kept "on life support" using molecular oxygen stored in cerebral liquid. The Mii'Ari loses consciousness during this period, effectively feigning death and allowing the symbionts, or any allies in the vicinity, to restore the rest of the body to working order.