With a grain of salt

 

When we don't believe a word of what somebody tells us, "take it with a grain of salt."

There was a time, however, when an ancient ruler thought it wise to put a real grain of salt into every drink offered him as an antidote to any poison that might have been put into it by a spy planted into his domestic service by his foes.  This ruler was named Pompey, the Roman general and politician who was defeated by Caesar and murdered in Egypt.  Pompey was so meticulous about his ritual that he carried with him his own supply of salt.  

It is from Pompey's use of salt as an antidote that we obtained our figurative expression.