I frequently post in AskLemmy so I think about questions a lot. For example, I was thinking about this in the shower and I was thinking “I really like this handmade soap. It’s much better than the usual stuff we get” and then I came up with a related question: “What is something that you would rather buy handmade instead of mass-produced?”
Which set contains no elements?
Or, more in the spirit of OP’s observation:
What are the fundamental rules for set theory?
You have to go more Im13andthisisdeep with it:
‘When a set has no elements we call it empty. It’s always unique, but contains nothing inside it. What is something else in your life that is also so simple and empty, yet utterly unique?’
Then you wait for a hundred replies, 50 listing various containers that are special to them and the other 50 telling you it’s their soul that’s empty.