with a grain of salt
Also, with a pinch of salt. Skeptically, with reservations. For example, I always take Sandy's stories about illnesses with a grain of salt—she tends to exaggerate. This expression is a translation of the Latin cum grano salis, which Pliny used in describing Pompey's discovery of an antidote for poison (to be taken with a grain of salt). It was soon adopted by English writers.