Because KCS wanted a sequel, and Holmes as a cat was too cute NOT to make a mini-series . . .
"How much longer is this going to last?" Mycroft grumbled from the bear skin rug. "I have pressing work in Whitechapel."
"Have Watson send a physician's note; he's still able to write," Sherlock suggested, delicately batting tobacco into the bowl of his pipe with his paws.
Watson glared mildly, having already played nurse-maid to four cats for almost two hours. Even Mrs. Hudson had to concede defeat when it came to opening the icebox for milk. Nevertheless, Watson found Holmes's suggestion appealing since it would get him out of the flat for awhile. One or two cats in open areas were no hardship; four cats in close quarters was having a particularly adverse effect on his eyes and nose.
Holmes was engrossed in carefully positioning a match between his teeth and its strike-box between his paws, ignoring his brother's muttered warning of, "you're going to end up singeing your whiskers, you know," when Watson slipped on his coat and hat.
"We shall try to endeavor to keep our shedding to a minimum while you are gone," Holmes slurred. "I am shorry I didn't notice your allershies before."
"Didn't you?" drawled Moriarty, rubbing against Watson's chair.
Watson fixed him with a glare before addressing Holmes. "I'll be fine, so long as you stay in the sitting room and out of my bedroom."