What would you say? Pen or A pen?

Hi,

Sorry for this slightly stupid-sounded question.

What would you say if a guy asked you, "what's this?" holding a pen in his hand? Is there any possibilities that you might say, "pen" instead of "a pen"?

I am asking this because it's hard to imagine you would say, "chicken" when he's holding "a chicken." So, I think I am just wondering if the same applies to something like pens.

Thank you,
M