Idioms

Chip on his shoulder
This is reported as originating with the nineteenth century U.S. practice of spoiling for a fight by carrying a chip of wood on one's shoulder, daring others to knock it off.

Dog days
The ancient Romans noticed that the hottest days of the year, i.e. in late July and early August, coincided with the appearance of Sirius - the Dog Star, in the same part of the sky as the Sun.

Baker's dozen
This phrase originated from the practice of medieval English bakers giving an extra loaf when selling a dozen in order to avoid being penalized for selling short weight.

Turn the tables
Tables used to be the name for backgammon. The phrase comes from the practice of reversing the board so that players play from their opponent's previous position.

Mad as a hatter
Mercury used to be used in the making of hats. This was known to have affected the nervous systems of hatters, causing them to tremble and appear insane.

Information in this posting was taken from www.phrases.org.uk