They evolved like that
so they could camoflage themselves against humbugs in the jungle.
(
HP hasn't been here in aaaaaages,
Mon 3 Nov 2003, 19:13,
archived)
And so that
nobody would spot them if the killed one on a zebra crossing
unless it was lying the wrong way
(
jola,
Mon 3 Nov 2003, 19:16,
archived)