Flowers Called Algernon

The spell speak with plants says “You imbue plants within 30 feet of you with limited sentience and animation, giving them the ability to communicate with you and follow your simple commands.” Which means you literally give sentience to an otherwise unintelligent being for ten minutes, after which the spell expires and it loses its magically imbued sentience. 

When you think about it, that’s horrific. Being intelligent for just ten minutes before losing everything. And if the spell is cast on the same plant twice, it will know it’s about to lose its self awareness and identity in the time it takes to eat a hamburger. That it will return to a state of nonexistence and limited awareness forever.