People
There is no doubt that Jeeves's pick-me-up will produce immediate results in anything short of an Egyptian mummy.
— P.G. Wodehouse • The Inimitable Jeeves

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
This is a joke built on exaggeration. Jeeves's restorative drink is praised as so powerful that the only thing it might fail to revive is a centuries-dead mummy. The absurd exception is the punchline, and it makes the tonic sound almost miraculous.
Context reviewed