Daphne puts on her galoshes while sitting on a brick wall which wasn't there before.
Before going into the sewer, Daphne and Velma put on Daphne's special "wallowing galoshes". Yet when they get flushed out of the sewer, Daphne and Velma are wearing their usual footwear instead.
The gargoyle could not be ticklish, as it is only a costume.
Velma tells Fred that the coin he put in the telescope is a Franc, but France had switched to the Euro in 2002, three years earlier. (This may have been overlooked deliberately to make a pun about Fred's voice actor Frank Welker.)
Fred knows the gargoyle is ticklish despite Shaggy not having mentioned it.