Awake this morning in the wee small hours I fell to thinking. Next to me lay two dogs, two cats and my husband. On the floor in their own baskets lay two more dogs. All, apart from me, were sleeping peacefully and dreaming, twitching and occasionally whimpering (non-humans) or muttering (human).
I sighed gustily. One of the dogs sighed. My husband sighed. I sighed several more times. I would have tossed and turned had I not been pinned down by mammals small and large (though not my husband). I sighed once more and then wondered, 'Have I ever heard a cat sigh?' I suppose I must have done, if cats do sigh and there seems no reason that they shouldn't. It's just that I can't recall ever hearing a cat sigh.
I fell asleep while thinking about this, so, useless pondering though it may have been, it was soporific, just like lettuce.