I think this one takes the cake. (Sadly, I have only a summary, since I can't afford the requisite trip to Canterbury just now.)
Between the coffin lid and the roof of the tomb was a space of about a foot, and once a poor fat madman somehow squeezed himself through and lay down on the coffin. The monks thought they would have to smash the whole thing to remove him, but miraculously he squeezed himself out.
You Must Be This Thin [--] To Touch The Relics.
No Fat Madmen Allowed.
Only People 10 Stone Or Less May Cross This Line.
Please Do Not Put Yourself Into The Tomb.
If You Fall In/Down, Please Be Advised That Help Cannot Be Provided. Sincerely, Mgmt.
Be Advised: If You Damage The Tomb And St Becket Repairs It Miraculously, You Will Be Charged 1d. For Inappropriate Use of Saintly Powers.