apparently they are necessary for living.
Wikipedia has lots of good advice on the subject.
[Food=biscuits]
[Water=tea]
(
Dr Scunner She’s a he, technically, but she’s scalding hot,
Tue 15 Apr 2008, 13:42,
archived)
I think I heard of them once
(
Mrs Trellis GIN,
Tue 15 Apr 2008, 13:44,
archived)