I thought this is just a plain tumbler. Then, I read the description and read something about scratching it. I didn't want to at first because I thought it would ruin the tumbler then I was surprised to see what happened.
My girlfriend was surprised to see this tumbler. At first, she was disappointed because I gave her a plain tumbler. Then, I told her to scratch it. She became skeptic and then she was surprised. She likes it now!