After telling Barnaby that they're witches, Sabrina does a little magic to dry up themselves and the bathroom. As she does this, Gwen's arms change position from hanging down by her side to folded.
As the newly-legged Barnaby is picking stuff out of a garbage can, the same guy can be seen walking by Gwen AND walking in the background behind Barnaby at the same time. He's the guy in the Hawaiian shirt with a baby blue towel around his neck and a royal blue baseball cap on.
When Sabrina jumps into the water to swim to a boat, right before she hits the water, it's very clear that her hair's already wet.
After their diving expedition, Gwen and Sabrina surface near a boat with "9254QD" written on the side of it. They go back under the water to find Dr. Martin, and resurface at the exact same boat which he is now on.