Extracted from the original commentary document by: aliyaist
The author writes:
Remember when it was Margaret who was in this exact position?
Open the two strips side by side. The first person who sends me a list of ten differences between them (other than Gwenyth, of course) wins a Postcard t-shirt.
EDIT: Well, that was fast. Reader TheElderLady submitted it less than three minutes after the strip was posted. She claimed to have figured it out using something called the "Magic Eye method".