The redbreast, “sacred to the household gods.” The legend says if a redbreast finds a dead body in the woods it will “cover it with moss.” Drayton alludes to this tradition
Covering with moss the dead's unclosed eye, The little redbreast teacheth charitie.
Shakespeare makes Arviragus say over Imogen-
“Thou shalt not lack The flower that's like thy face, pale primrose; nor The azured harebell ... the ruddock would With charitable bill ... bring thee all these.” Cymbcline, iv. 2.
So also in the folk tale of The Babes in the Wood-
The Robins so red Fresh strawberry-leaves did over them spread.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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