She escorts him to the "sick room" for a lie down as he looks in imminent danger of fainting. She even gets him to look in the mirror to see if he can spot the close resemblance to Nosferatu the vampire. But the boy is adamant that he is not feeling ill.
Being a tenacious lady, the depute keeps considering the matter and then, drawing on her previous experience in home economics, asks the killer question: "Have you got a new duvet?"
He's amazed at her perspicacity: "Er, yes miss."
"Is it green?"
"How did you know, Miss?" (wide-eyed with admiration).
Confucious he say: Boy who sweats under new green duvet all night comes to school in morning looking like Christopher Lee.