Maccas held a recent promotion whereas they offered plastic Furby toys along with their Happy Meals. There are 80 of these to collect, and these are only available in Maccas in the U.S.
Each of the 8 different sets (consisting of ten different coloured Furbys) have different functions. As you can see from these pics they are all as brightly coloured as a radio-active sea slugs on steroids.
Anyway, the eight different functions are:

Set 1

Push Furby's tail and he'll growl and move his eyes

Set 2

Push him forward, and if he doesn't fall off the table and smash he'll move his ears and feet. Shock, perhaps?

Set 3

Pull Furby backwards, and if you don't break his neck he'll roll back forward.

Set 4

Press Furby's feet, and if he's got ingrown toenails he'll squeal, if not he'll move his mouth, eyes and ears.

Set 5

Furby says Eek!" when you turn him upside down. Too many Chocolate thickshakes....

Set 6

Press his little tail and he'll cover his eyes in a "peek-a-boo" fashion.

Set 7

Press his tail and this time he'll squeak and move his eyes and mouth.Talented little fellow....

Set 8

You can all thank Twan, a Topsy Furby viewer for this information! Twan owns a Furby named May Lah Kah and a Bud called A Loh May Lah. Thanks heaps for the info Twan!

Twan says that Set 8's function is:

A roller-ball moves Furby's eyes and ears.