■漫畫&說明︰英國文化協會
The first woman is saying that she has bought the kitten as a present for her sister. Her friend understands that she has got the kitten "for" her sister (meaning she has exchanged her sister for the kitten), and is surprised that someone would agree to swap a kitten for a human!
誤解是由for字而起：for可以指「給」，也可以指「以......代替」。女孩的朋友以為她以妹妹或姐姐交換了小貓回來！
逢星期五見報