How can I get free food at McDonalds?

Okay, on Monday, I walked into one of my local McDonalds locations to get a beloved strawberry banana smoothie and expected to spend $2.95 on it. Well when I went to order it at the register, I told the lady I wanted a medium strawberry banana. I was a little shocked to see that the total was $2.75 instead of $2.95. Seconds later, the lady said here you go and she gave me a medium chocolate shake. I said Miss, I ordered a strawberry banana smoothie and so she had one made for me. She let me have the shake too. I was thrilled to pay only $2.75 for a shake and a smoothie. I aint no theef, I iz like a good citizen...but I wanna have it happen again. Should I say chocolate shake and then when I get it, say I asked for a smoothie? Please help me