From Creatures Wikia
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).