There are times when you have to be dishonest with your feline friend. When you give them a treat and then have to put them in the carrying case. When you have to hide medicine in their wet food even though they do not like the medicine. Or when you have to trick them out of the back of a cabinet because they'll get stuck in there again!
But do your cats know? Can they sense when you are lying?
Do cats know when we're lying?
Yes and no.
Cats are not living in their own cat world with no regard to others. You are just living in their cat world with them.
Cats have been found to perceive emotions and do tend to look to their owners for a gauge of how they should be reacting. However, that is exactly their perception of us. They don't necessarily care in a huge way about how you are feeling for your sake. It is more about how your feelings affect them.
Additionally, cats don't really have a sense of "telling the truth," in the same way we do. However, they can sense when something important to them is amiss, e.g. if there is gross-tasting medicine in their food, to use the example from above. You might find that sneaking medicine into your cat's food works once, and then never works again, because your cat caught onto your trick.
How do cats perceive humans?
Unlike dogs, cats don't perceive us as entirely different species than them. They see us more as large clumsy cats because we trip over them constantly and they trip over us hardly ever (but if you ask a cat, they'll say never). We are their cat pack, and so they treat us like they would treat any other cats they are living with (which is why they sometimes groom us and sit beside us).
When cats in the wild live in groups, they have come to learn that how the group reacts is the best way to survive. That's why when you are frightened or upset, your cat is likely to be jumpy and scared. When you are calm and smiling, they are more likely to be more at ease. This is why when you are happy. your cat is more likely to be happy.
On the alternative side, when you are upset, your cat can usually sense that and is disturbed by that. They might even try to cheer you up to make the world right again, for you and for them. However, this is only the case with humans that they live with. Strangers are a different matter because strangers are not a part of the pack. Unless the cat lives with the human, they don't trust the human until said human has earned their trust.
Many believe cats don't react at all to us. However, that is far from the case. Cat reactions just tend to be more subtle than, say a dog jumping up and down when they are happy. Very few cats jump up and down with joy, although they might get the zoomies when a can of tuna is opened. Cats show "positive" reaction in smaller ways when they trust you, by doing things like purring, or rubbing against you. Negative reactions are also subtle, like tense body positions, or flattened ears and specific tail movements. These actions are ways that tell you whether or not your cat feels comfortable and trusting in a given situation.
Your cat can't necessarily tell from your voice or expressions that you aren't being honest. They usually won't catch you in a lie. For example, if you're smiling and using a calming voice, your cat might believe they should trust you at that moment. However, cats are not quick to forgive. When tricked or mistreated, not only do they remember, but they now distrust you. Which means once you lie, it is hard to trick a cat again because they remember how you did it, and won't let it happen again—especially if it involves food.