I told you to pick something you don't know and have not thought about...
No, you did not. You said, and I quote, "Did you know there is a blue star called: "Alcyone"? (if you do, insert something else you don't know, how many teeth a Tyrannosaurus have etc.)". I don't know how many teeth a t-rex has, so I picked it, as per your instruction. You never said, as a condition of the picking, that it's something I should never have thought about. In fact, had you made that request, the conversation would have gone very differently. Why is that? Glad I asked!
If you ask me to pick something to talk about I've no knowledge of and have never heard of, that's a logical impossibility. Why? Because I've never heard of it! I know even know it exists, so how can I possibly pick it? How would it be possible for me to pick something I have no concept of, don't know anything about, whether or not it exists, etc?
The reason for that is that you are asking about a specific item but are forgetting there is knowledge of a class of items. If, say, for instance, I don't know about a specific star, I am aware of stars, galaxies, particles, how stars in general work, their lifecycle, etc.. The same for dogs, dinosaurs, etc. I have at least general knowledge of these things. You are asking me pick something in a class that by definition is completely outside of my realm of all knowledge or concept of any type. By definition I cannot pick something in that class of items.