Look like the innocent flower, but be the serpent under't (1.5.74-5)
Some editors believe these lines derive from Virgil's Eclogues 3.93,
You, picking flowers and strawberries that grow
So near the ground, fly hence, boys, get you gone!
There's a cold adder lurking in the grass.
In The Royal Play of Macbeth (the most fascinating and convincing book I have ever read on Shakespeare's authorial intention) Henry Neill Paul explains that these lines are an allusion to arguably the most significant moment in Shakespeare's time, the discovery of the Gunpowder Plot.
To commemorate the discovery of the heinous scheme, King James had a medal created picturing a serpent hiding amongst flowers. Every person watching Shakespeare's drama in Jacobean England would have understood immediately the context and weight of such an allusion.
How to cite this article:
Mabillard, Amanda. Macbeth Glossary. Shakespeare Online. 20 Aug. 2000. (date when you accessed the information) < http://www.shakespeare-online.com/plays/macbeth/macbethglossary/macbeth1_1/macbethglos_innocentflower.html >.