A patron walks up the the desk with some big plant parts and asks, "do you know what this is? It's a great big bush in my cucumber patch."
I'm not great at plant identification. While I was considering the best approach, the patron pulled out two more pods like those on the plant, except that they were dried and the seeds inside rattled when he shook them. He kept saying that he's never seen seed pods like that on a weed before.
Between the websites we looked at and a few plant books we had on the shelf, the patron was torn between considering this an "invasive weed" or an "ornamental flower" (which reminded me of something a friend's dad once said: a weed is any plant that's growing where you don't want it to grow).
In the end, the patron decided to pull them all out, and happily left us what he brought in as "a bouquet for the staff." I was happy too, because this is one of those questions that could have taken all day to answer - it's nice to get lucky once in awhile.