Cats communicate mostly through body language, not vocalization — meowing is largely a behavior cats developed specifically to communicate with humans, not each other. Learning to read the signals below will tell you more about how your cat is feeling, moment to moment, than almost anything else.
Tail
A tail held straight up, sometimes with a slight curl at the tip, is a friendly greeting — this is one of the clearest positive signals in the feline repertoire. A low or tucked tail suggests anxiety or fear. A tail thumping or lashing side to side is a sign of irritation or overstimulation, and is often misread as playful — if you see this while petting a cat, it's usually a cue to stop. Puffed-up tail fur (piloerection) signals fear or a startle response.
Ears
Forward-facing, relaxed ears mean a calm, interested cat. Ears rotated sideways or flattened back ("airplane ears") indicate irritation, fear, or the early stages of defensive aggression. Watch the ears alongside the tail — the two together give a much clearer picture than either alone.
Eyes
A slow blink directed at you is a genuine trust signal, sometimes called a "cat kiss" — try slow-blinking back. Dilated pupils can mean excitement, fear, or arousal depending on context (the rest of the body tells you which). Fully constricted pupils in normal lighting can indicate agitation.
Body posture
A relaxed, elongated body with exposed belly is a sign of deep trust and comfort — but this is not, contrary to popular belief, an invitation to rub the belly; many cats find belly touching overstimulating regardless of how relaxed they look. A crouched, tense body with weight low to the ground signals fear or defensive readiness.
Putting it together
The most useful skill isn't memorizing single signals but reading combinations. A cat with a puffed tail, flattened ears, and dilated pupils is frightened and needs space, not comfort. A cat with an upright tail, forward ears, and a slow blink is inviting interaction. When signals seem to conflict, the safest interpretation is usually the more cautious one — give the cat the choice to approach rather than approaching further yourself.