Dogs in their wild state never bark; they howl, whine, and growl, but do not bark. Barking is an acquired habit; and as only domesticated dogs bark, this effort of a dog to speak is no indication of a savage temper.
Barking dogs seldom bite. Huffing, bouncing, hectoring fellows rarely possess cool courage. French: “Tout chien qui aboye ne mord pas.” Latin: “Canes timidi vehementius latrant quam mordent.” Italian: “Can che abbaia non morde.” German: “Ein hellender hund beisst nicht leicht.”
To bark at the moon. To rail at those in high places, as a dog thinks to frighten the moon by baying at it. There is a superstition that it portends death or ill-luck.
I'd rather be a dog, and bay the moon, Than such a Roman.
Shakespeare: Julius Cæsar, iv. 3
His bark is worse than his bite. He scolds and abuses roundly, but does not bear malice, or do mischief. The proverb says, “Barking dogs never bite.”
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894