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,
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-grace o' Sundays: O 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)
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?