From the odd looks Derrick was getting from his family, he realized they had not stopped because they recognized him. His Mom was blushing, and he noticed some grins on many of the guests' faces. He finally remembered that he was naked, and looked down to see his stallion's cock pushing out from its sheath, the massive testicles hanging swollen underneath. Even that was not all, though. Muscles pulled in his rump, and he twisted around to see an equine tail emerging over his rectum.
Spotting a mirror on the side wall, he clopped over and stared. The change to a stableboy had not stopped, only slowed. The creature staring back at him was almost identical to the servant beasts he had seen in the stable, and even as he watched, he could see his face pushing out and his eyes getting larger. There was nothing recognizable about him any more, hardly enough to mark him as having been human.
One of the satyr staff members came over beside him and bleated "You'd better stop before your guest status is revoked."
Derrick gave him a confused look. The goat-like humanoid shook his head and said "This change is all your doing. You must have liked the stableboys - this resort lets you be whatever you want to be. You must want to be one of the stableboys, but if you go all the way you'll think like one, too. That means living to serve centaurs and other equines. If you don't stop before that, you'll spend the rest of your vacation happily shoveling manure." The satyr hesitated and then added "And by then, going back to being human won't be something you will want."