Several common cat behaviors have specific origins in feline biology, once you know what to look for.
Kneading traces back to nursing behavior in kittens, stimulating milk flow from the mother. Adult cats that knead blankets or laps are generally displaying comfort and contentment, a leftover instinct from kittenhood.
Headbutting, or “bunting,” is scent-marking behavior — cats have scent glands on their face, and headbutting a person or object is a way of marking territory and showing affiliation simultaneously. It is widely considered a strong sign of trust and affection.
Showing the belly is more nuanced than it looks. Unlike dogs, cats showing their belly are not necessarily inviting a belly rub — it is more often a sign of deep relaxation and trust in the immediate environment. Many cats will react defensively if the belly is actually touched, despite the relaxed display.