Meaning:To take a statement with 'a grain of salt' or 'a pinch of salt' means to accept it but to maintain a degree of skepticism about its truth.
The idea comes from the fact that food is more easily swallowed if taken with a small amount of salt. Pliny the Elder translated an ancient antidote for poison with the words 'be taken fasting, plus a grain of salt'.
Pliny’s Naturalis Historia, 77 A.D. translates thus:
After the defeat of that mighty monarch, Mithridates, Gnaeus Pompeius found in his private cabinet a recipe for an antidote in his own handwriting; it was to the following effect: Take two dried walnuts, two figs, and twenty leaves of rue; pound them all together, with the addition of a grain of salt; if a person takes this mixture fasting, he will be proof against all poisons for that day.
The suggestion is that injurious effects can be moderated by the taking of a grain of salt.
The figurative meaning, i.e. that truth may require moderation by the notional application of 'a grain of salt', didn't enter the language until much later, no doubt influenced by classical scholars' study of Ancient Greek texts like the works of Pliny. The phrase has been in use in English since the 17th century.Sources:
http://www.phrases.org.uk/meanings/take-with-a-grain-of-salt.html
http://moneyandblogging.files.wordpress.com/2009/06/grain-of-salt.jpg
http://www.american.com/graphics/2008/february-02-08/Salt%20feature.jpg
The story that lies behind 'stealing someone's thunder' is that of the literary critic and largely unsuccessful playwright, John Dennis. In 1704, Dennis's play Appius and Virginia was produced at the Drury Lane Theatre, London and he invented a new method of creating the sound of thunder for the production. We don't know now what this method was (some texts say it was a refinement of the mustard bowl referred to by Pope, in which metal balls were rolled around in a wooden bowl), but it is reported that after Appius and Virginia failed and was closed, the method was soon afterwards used in a production of Macbeth. Dennis was less than pleased at having his idea purloined and this account of his response was recorded by the literary scholar Joseph Spence (1699–1768) and later quoted in W. S. Walsh's Literary Curiosities, 1893:
