Powdered root of what to an infusion of what? Harry glanced at Ron, who looked as stumped as he was; Hermione’s hand had shot into the air.
“I don’t know, sir.” said Harr
Asphodel symbolically means death, esp. death of someone beloved to the person who offers asphodel. Asphodel is also a lily. Wormwood symbolically means bitter sorrow. So in essence, Snape is asking Harry if he knows what death wrapped in bitter sorrow is. Or put another way, he might be trying to tell Harry that he loved her and that he bitterly regrets Lily’s death.
Harry, of course, ignorant of not just the wizarding world, but of symbolism, feels the clue-by-four whizz over his head and begins to wonder why Snape appears to be singling him out for abuse.
Snape, of course, feels Harry (whose mother was a Potions prodigy) is being remarkably obtuse and/or possibly spurning his carefully couched condolences.
In essence, what these interpretations tell us is that it’s possible that Snape is not taunting Harry at all, but is rather giving him symbolic information, possibly even condolences on the loss of his mother.
http://corvus-kari.dreamwidth.org/307595.html
https://expatronum.wordpress.com/2010/04/26/asphodel-wormwood-bezoars-and-aconite/
