What sort of mad scientist doesn't experiment on humans?
A mad scientist that's watched enough movies to realize that giving your psycho serum to humans (or God forbid, your own most evil minions or criminals) will invariably wind up with their psycho turning on them.
Hence, use your serum on something small, cute, and easily distracted with a ball of yarn or some Whiskas kitty treats no matter how powerful it gets.
When a human received elements from other creatures....Ah, yea...It's just common sense!!This cat is... the prototype?But, as a matter of course...That's why, everything will be fine as long as we experiment on a non-human!!...Um...?...Let me explain...They evolved into an existence beyond human understanding.In other words, a monster!!That sort of process involves various kind of risks.In other words, he's a SUPER CAT!!My Mr. X has been granted human intelligence and physical capability!