Everyone is familiar with a situation where your conversation partner mentions an idea or a topic that you just can't stop thinking about for days without end.
To quote an economist Robert Lucas Jr.
Is there some action a government could take that would lead the economy to grow[...] once one starts to think about them, it is hard to think about anything else.
In my mother tongue (Slovak), there is a phrase for such an experience, literally translated as "planting a worm in someone's head".
Is there any such phrase/idiom in English?
Planting an idea is a very close substitute, but it communicates a (usually malicious) intent in doing so.