In Harry Potter and the Philosopher's Stone, the first thing Snape asks Harry in Potions class is:
"Potter! What would I get if I added powdered root of asphodel to an infusion of wormwood?"
According to the Victorian Language of Flowers, asphodel is a type of lily meaning 'my regrets follow you to the grave' while wormwood means 'absence' and symbolises bitter sorrow. The entire question has a hidden meaning of "I bitterly regret Lily's death."
— Quora user Yilise Lin