I thought this little green stick thing at Starbucks was a stirrer (and it kind of still is) until I saw someone do this with it and I learned that it is designed to fit perfectly to close the sipping hole and make this a no-spill top!
Go ahead. Tell me. Did you already know this???
Jane's Lessons Learned 
I knew this! I use it occassionally but think they are pretty wasteful.
Hi jane, I did know this, and I had also heard that the designer of this made a killing. Wish I could think of such a small and silly little thing and hit a jackpot.
I had no idea! Wow!
Yes.
I did know this, after Teresa told me!