Cats and humans are built much the same way and share many of the senses - sight, hearing, smell, taste, touch - as well as having additional "senses" which are adaptations to our particular environments and lifestyles (e.g. the Flehmen taste-smell reaction in cats). Though humans have better vision, cats have better smell, taste and hearing. Like us, cats feel heat, cold, pain and other physical sensations. Physical stimuli may lead to physiological responses, some of which are termed emotions. If humans and cats have similar responses to, for example, the smell of enticing food, they may share certain emotions e.g. happiness at the prospect of a satisfying meal.
One of the most obvious animal emotions is pleasure. It is evident when your cat snuggles up purring and when it plays. Although play is an important part of learning and honing life skills in youngsters, it is quite obviously also fun otherwise adult cats wouldn't bother playing. There is some evidence that playing, or at least the physical exertion aspect of play, releases "feel-good" hormones in the brain, giving a sense of wellbeing. When rats play, their brains release dopamine, a neurochemical associated with pleasure and excitement. When a rat anticipates a play session, dopamine is released, making it active, vocal and excited (the effect of this can be seen by dosing rats with dopamine-blockers). Happy rats also produce opiates, another feel-good neurochemical.
Owners rely on feline behaviour and body language for clues about its emotional state. In this respect, dogs are considered to be more expressive than cats. Dogs evolved elaborate systems for social communication in a pack; the human household is a surrogate pack, therefore dogs communicate with owners as they would other dogs. Dogs transfer their dog-to-dog social behaviours into dog-to-human communication. Many dog owners misinterpret the submissive or juvenile behaviour of a lower-ranking dog (towards its higher ranking owner) as affection.
The predatory instinct is hard-wired into the feline brain (electrical stimulation of a particular brain region triggers pouncing behaviour). Pet cats sometimes take prey home, either as a food gift for its surrogate family (in this respect the cat is relating to owners in the way a mother relates to kittens) or because the house is its den and hence a place to eat in safety and at leisure.
Cats show fear and lust in response to the appropriate sights, sounds and smells, but love requires a degree of abstraction which cats probably do not possess. Lust is the mating urge, love is the emotional baggage which surrounds and tempers that urge in most humans. Humans have a wider range of emotions and the emotions which we share with cats are more refined in the human species.
A cat which has fallen off a shelf in plain sight will pretend the event has not happened i.e. that it has not shown any weakness. A human may make excuses for why a similar human mishap happened (the ledge was icy or slippery); this is simply a human way of saving face. Cats speak with their bodies and an "embarrassed" cat will most often sit down and wash nonchalantly - cat speak for "nothing has happened"!
Grief has also been observed in many wild species following the death of a mate, parent, offspring or pack-mate. Feline grief at the death of a long-term human or feline companion can include severe mental disturbance. Grief varies according to the individuals and some cats show little grief while others can be deeply traumatised. This variability leads some scientists to insist that observation of grief in cats is anthropomorphism on the part of the owner. Such scientists forget, or ignore, that fact that humans are equally variable in how they express grief.
When owners say their cats are jealous, they are trying to rationalise a feline emotion into human terms. Feline "jealousy" may be a response to any number of stimuli - the cat seeking to better its place in the household hierarchy or an opportunist or stronger cat competing for food or attention. The cat does not rationalise it in terms of "I am jealous of the other cat" or "I covet what the other cat has"; its feelings will be more along the line of "I am stronger or fitter than the other cat, I deserve to be dominant cat around here." Cats are not as strictly hierarchical as dogs, but where several cats live in a single household, they will establish a pecking order.