Watson had opened the door to the sitting room so the cats were free to roam into the hall and kitchen. This kindness didn't impress Moriarty, who couldn't rejoin his crime network in his new body and was put out by it. Not that he blamed Watson personally, but as the only one still human, Watson had to suffer some misery also. Moriarty's revenge was to try to shed on Watson's chair and desk as much as possible until Holmes, Mrs. Hudson, and Mycroft let him know in no uncertain terms that there would be no more such activities.
The ginger cat sulked in a far corner but behaved himself the rest of the evening, giving Watson a wide berth. However, once darkness descended and Watson retired for the night, Moriarty found a pressing need to yowl incessantly. The combined efforts of three determined cats were no match for an equally determined cat's lung-power.
Finally, after almost an hour, Watson stomped down from his room in his dressing-gown, murder in his eye. He seized Moriarty by the nape of the neck. Before the professor could try to sink his fangs or claws into Watson's flesh, the doctor gave him a spoke in a low, deadly earnest voice.
"Keep that up and you'll be on the receiving end of a rugby bomb-kick."