Symbolism, Imagery, Allegory
When Ophelia loses her mind in Act IV, Scene v, she starts handing out flowers to everyone around her. Sure, she talks directly about the symbolic meaning of those flowers, but what's also important is who might be getting these flowers.
There's rosemary, that's for remembrance.
Pray you, love, remember. And there is pansies,
that's for thoughts. […]
There's fennel for you, and columbines.
There's rue for you; and here's some for me; we
may call it herb of grace o' Sundays. You must wear your
rue with a difference. There's a daisy. I would
give you some violets, but they withered all
when my father died. (4.5.199-201, 204-209)
Fennel symbolized strength and praiseworthiness, columbine symbolized folly, daisies symbolized innocence, and violets symbolized faithfulness and modesty. So which flowers belong to which characters? Does Ophelia give the rosemary (for remembrance) to an invisible Hamlet, praying he hasn't forgotten about her? Does she give the rue (another word for regret) to Gertrude, who may be regretting her hasty marriage to Claudius?
And if she's with-it enough to match the right flower to the right character, how crazy is she, really?