The Health & Safety bods are interrogating Frog.
"Are you the only first-aider in the building?"
"Do you think that's enough?"
"Ah," interposes T.Aldous, "Sybil's going to be the other first-aider but she's on leave when the course is being run."
Later on, Frog asks Sybil the obvious question:
"Have you been on leave for the past four years?"