The Hippy Norns are a genetic breed for Creatures created by Lis Morris. They reduce their drives by using glycogen. To compensate for this, they are "fed" by anything that reduces their Need for Pleasure - for example, tickling. They also tend to be very interested in fiddling with toys, as they are rewarded for doing something to reduce a drive - like boredom - even if they do not need it reduced.
Exported Hippy Norns can be downloaded (archive) at The Palace of the Evil Shee. For a detailed discussion of the origin of the Hippy Norns and their biochemistry, see the Hippy Norn home page and breeder's guide (archived). Pain and boredom seem to be the factors which reduce hippy norns' health the most.