Answer: I would contend that the right answer is the A) "terrible baying sound."
Explanation: Just to elaborate a little on the answer, it can be added that an ominous scene is suggestive of an unpleasant event that is about to happen. The facts that the dogs were numerous and enormous (option B), that they were bounding into the barn (option C), and that Snowball sprang just in time (option D) are not necessarily suggestive of an upcoming unpleasant event. A terrible baying sound, however, does suggest a threatening sign.