Apologies for the confusion, it was Somhairle doing all the growling. I haven't captured Oisín’s peculiar noise yet on camera. The sound in that video seems rather faint to me, I'll have to record a better example.
Somhairle just growls over cat food. There is a large toy butterfly hanging on an elastic string from the bathroom door. Whenever Somhairle ‘catches’ it, he growls as at cat food time, then tries to run off with the butterfly. Of course at some point, due to the magic power of the elastic, the butterfly comes back to life and escapes from his jaws and flies back to the door.