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.