A sly and constant knave, Not to be shaked; the agent for his master And the remembrancer of her to hold The hand-fast to her lord. I have given him that Which, if he take, shall quite unpeople her Of liegers for her sweet, and which she after, Except she bend her humour, shall be assured To taste of too.
A sneaky and loyal villain, Not easily shaken; the agent for his master And the reminder to her to keep Her promise to her husband. I’ve given him that Which, if he accepts, will completely ruin her Of suitors who seek her love, and which she, later, Unless she changes her mind, will be certain To suffer from too.
The Queen · Act 1, Scene 5
The Queen, having given Pisanio the poisoned box to deliver to Imogen, reflects on him in soliloquy as a servant she can trust precisely because he is disloyal to everyone but his master. The line lands because it reveals the Queen's own blindness—she believes Pisanio will follow orders from her when his entire nature is devoted elsewhere. It shows how those who deal in deception mistake loyalty for corruptibility.
[Aside] I do not like her. She doth think she has Strange lingering poisons: I do know her spirit, And will not trust one of her malice with A drug of such damn’d nature. Those she has Will stupefy and dull the sense awhile; Which first, perchance, she’ll prove on cats and dogs, Then afterward up higher: but there is No danger in what show of death it makes, More than the locking-up the spirits a time, To be more fresh, reviving. She is fool’d With a most false effect; and I the truer, So to be false with her.
[Aside] I don’t trust her. She thinks she has Strange slow-acting poisons: I know her nature, And I won’t trust her with A drug of such a dangerous kind. The ones she has Will dull the senses for a while; She may first test it on cats and dogs, And then move to something higher: but there’s No real danger in the death it appears to cause, More than just locking the spirit away for a while, To refresh and revive it. She’s fooled By a very false result; and I am the wiser, So I will deceive her in return.
Cornelius · Act 1, Scene 5
Cornelius the doctor has just given the Queen what she believes are deadly poisons, but he has secretly substituted harmless sleeping draughts that will only mimic death. He speaks these words to himself, knowing her malice and doubting her claims about needing them for animals. His moral defiance in this moment saves Imogen's life and ensures the Queen's own treachery will not succeed as planned.