Then the woman asked, “Whom shall I bring up for you?”
“Bring up Samuel,” he said.
12When the woman saw Samuel, she cried out at the top of her voice and said to Saul, “Why have you deceived me? You are Saul!” (1 Samuel 28:11-13).
After she sees the the apparition of Samuel she suddenly realizes that the man standing in front of her is really Saul the king of Israel. But the text doesn't give us a clue how she might have figured this out just from seeing Samuel's ghost? Saul had told her that he wants her to bring up Samuel (v. 11), so what has changed now that she saw Samuel, and how did that indicate that the man in front of her was none other than King Saul?
I saw a couple of explanations in Gill's exposition, (I'm also aware of Rashi's solution) but they are all unsatisfactory to me. From the text it seems that somehow the sight of Samuel itself gave away the secret that the man was Saul, not that there was some external feature that revealed this to her. I'm also looking for a solution that would take historical interpretation into account, and would shed light on how it may have been understood by the Israelite reading Samuel 3,000 years ago.