It happens that Andrew Mawson formulated :
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 ?

Yes, we have an 18month old BC, and her 9 year old big brother. She
seems to deliberately triggers him, just for the hell of it.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk