TO SEE A MAN ABOUT A DOG
This old saying first appeared in 1866 in a play by Dion Boucicault (1820-1890) called the Flying Scud in which a character makes the excuse that he is going ‘to see a man about a dog’ to get away.
STRIKE WHILE THE IRON IS HOT
This phrase comes from the days when blacksmiths lifted iron objects from the furnace and hammered it. They could only hammer the object into shape while the iron was hot, before it cooled down.