Built for low light
Cats are not colour-blind, but they do see colour differently from us. Their vision is dichromatic, meaning they perceive blues and yellows well while reds appear washed out, so a bright red toy may look far duller to them than it does to you. Where cats truly excel is in dim light: a reflective layer behind the retina called the tapetum lucidum bounces light back through the eye, and a rod-rich retina gathers what little light there is, which is why their eyes seem to glow in the dark. They are also superb at detecting movement, ideal for spotting the twitch of prey. The trade-off is that fine detail is weaker than ours, so cats read the world more through motion and contrast than sharp focus.
Hearing beyond ours
A cat's hearing is one of its most remarkable senses. It reaches well into the ultrasonic range, up to around 55 to 64 kHz, far above the limit of human hearing, and this upper range happens to match the high-pitched squeaks of the rodents cats evolved to hunt. Their ears are wonderfully mobile too, each able to rotate to pinpoint exactly where a sound is coming from. This is why a dozing cat can flick an ear toward a rustle you never noticed. When your cat seems to react to nothing at all, they are very likely hearing something genuinely there, just beyond your own range.
A world of scent
Smell shapes a cat's world far more than it shapes ours. Their sense of smell is highly developed and helps them assess food, territory and the other animals around them. On top of the ordinary nose, cats have a second scent tool: the vomeronasal, or Jacobson's, organ in the roof of the mouth. When a cat encounters a particularly interesting scent or pheromone, it may pull back its lips and stand with its mouth slightly open in what looks like a grimace, called the flehmen response, drawing the scent up to this organ. It is not disgust, but a cat savouring information we can't detect at all.
Whiskers and touch
A cat's whiskers, properly called vibrissae, are far more than decoration. They are deeply rooted, richly supplied with nerves, and sense subtle changes in airflow as well as the width of gaps, helping a cat judge whether it can fit through a space in the dark. Whiskers also reflect mood, fanning forward with curiosity or pinning back in fear, so they double as a window into how your cat is feeling. You may have heard of "whisker fatigue", the idea that narrow bowls stress a cat by bumping the whiskers; it is a popular notion but not well proven, so treat it lightly rather than as established fact. Either way, the kindest approach is to enrich your cat's world for all these senses, with things to watch, listen to, sniff and safely explore.