As Iris Silver Mist uses almost every iris molecule known to man, MKK uses more animalic material than any fragrance prior.
The basic animalics are listed below, and I'm sure there are more. But it's done with finesse, and it's relatively subtle in its delivery, very feline, and long and slow rather than hard and fast. It's a beautiful fragrance that gets better and better as it goes.
Five kinds of quality musk
Costus (animalic that smells like wet hair)
Ambrette (smells similar to animal musk)
Kiehl's is pretty, flowery, with some decent musk, but it's nothing like MKK.
L'Air de Rien uses a high quality musk (bolstered by a lot of oakmoss) that builds and maintains some relatively exquisite tension, but the animalics level out and the scent just begins to work its way into being a great oriental with solid animalic backgrounds. It's an excellent fragrance with some outrageously good sillage (see-yazh). And as someone wrote, it has the feel of an old flannel shirt well-worn and infused with some good healthy sweat. Sometimes I think of it as a softer, more oriental vintage Narcisse Noir (Caron).