For a system to oscillate you need positive feedback and a bit of phase
shift.

Our dogs oscillate ! The new 16 week old puppy 'hears something' makes a
very gentle 'almost bark' but really a growl, big sister responds with a
proper bark, to which puppy responds thinking 'well there MUST be something
out there'. So big sister, now hearing a proper bark responds again, and the
pair go off into a crescendo of woofing and barking which can be very
amusing, but not when you're on the 'phone. Anyone else have this ?

Andrew

ps lucky the nearest neighbour is half a mile away