Meaning: Excellent quality (or the small things in life that count)
Example: Those miniature gold bar earrings are the bee’s knees.
Origins: Various and undecided. Bee’s knees carry the awesome pollen. 

(Sources.)
Rewrites: the cow’s udders the sheep’s locks the bird’s peeps the hummingbird’s wings the puppy's cuddle the striker’s toes the punter’s feet the penitent’s knees
Discussion: I suggest there are few things so small that provide so much gold as the bee’s knees, but there are lots of things we probably don’t consider that proportionally provide an equal amount of good. That’s what I took into consideration in rewriting this cliché.