A punched card with all holes
punched (also called a `whoopee card' or `ventilator card').
Card readers tended to jam when they got to one of these, as the
resulting card had too little structural strength to avoid buckling
inside the mechanism. Card punches could also jam trying to
produce these things owing to power-supply problems. When some
practical joker fed a lace card through the reader, you needed to
clear the jam with a `card knife' -- which you used on the joker
first.
