I thought about this for a moment or two. What you are describing is quick reactions, while Quill is emphasizing the quickness and feeling. This is not a power (enhanced senses does not include reflex/speed), nor mutation.

Personally, I’m not even going to call it a mutation. Cat-like reflexes are not based off of cats themselves, but are instead used as a term to describe fast reactions. Similiar to someone calling another person a ‘snake’ because of their mischievous and backstabbing behavior. (Large = bear-like, bird = high dreamer, social butterfly  = eccentric, etc.) This person is not a snake, nor are they a cat. They are being compared to these animals because of the physical traits they have in common. Simply, cat-like reflexes (not abnormal, as super speed is not a power or mutations) means they are quick to react.

Hence this would be a trait to your character. Your character would be described as being quick to react to pressing situations or the littlest things, such as dropping a piece of prey and managing to catch it in their palm without another thought. If you are making a biography for your character, adding a physical traits section next to personality or body specifications would be very helpful for your readers.

Ooo this one is tricky. So I'm doing some research on the subject and this is what I've found so far:

Quote:Another factor in cats’ flexibility is that their shoulder blades are attached to the rest of the body only by muscles. Humans’ and dogs’ shoulder blades, on the other hand,form part of the joint that connects the upper arm or foreleg to the body. This allows cats to extend their running stride even more. Their loosely attached shoulder blades, along with tiny rudimentary collar bones, also allow them to squeeze into tiny spaces...

Quote:Moreover, the feline shoulder blade is attached to the rest of the body only by muscles, not by bone. [like canines... . And unlike the long anchored collarbone we humans have, cats have tiny rudimentary collarbones that contribute to their ability to squeeze through tight openings.

To restate, the spine is modified, so are their collarbones and shoulder blades. I would specify this within your tags, saying it is some sort of mutation, along with the explanation behind it. Whether that'd be under-developed spines, a rare recessive outcome, etc, is up to you.

No problem!!