Why do some cats hop up on their hind legs when greeting you?

One of the problems cats have when adjusting to human companions is that we are much too tall for them. They hear our voices coming from what is, to them, a great height and they find it hard to greet such a giant in the usual way. How can they perform the typical cat-to-cat greeting of rubbing faces with one another? The answer is that they cannot. They have to make do with rubbing our legs or a downstretched hand. But it is in their nature to aim their greetings more towards the head region, and so they make a little intention movement of doing this – the stifflegged hop in which the front feet are lifted up off the ground together, raising the body for a brief moment before letting it fall back again to its usual four-footed posture. This greeting hop is therefore a token survival of a head-to-head contact.

A clue to this interpretation comes from the way small kittens sometimes greet their mother when she returns to the nest. If they have developed to the point where their legs are strong enough for the 'hop', the kittens will perform a modest version of the same movement, as they push their heads up towards that of the mother cat. In their case there is not far to go, and she helps by lowering her own head towards theirs, but the incipient hop is clear enough.

As with all rubbing-greetings, the head-to-head contact is a feline method of mingling personal scents and turning them into shared family scents. Some cats use their initiative to re-create a better head contact when greeting their human friends. Instead of the rather sad little symbolic hop, they leap up on to a piece of furniture near the human and employ this elevated position to get themselves closer for a more effective face-to-face rub.