A childhood belief about sweeties

When my (twin) sister and I were like 5, we went to a day camp where they had us make cookies out of playdough and put them in the oven. While we were eating snack they’d switch them for matching real cookies and bam - magic! My sister really wanted to try this at home so Mom entrusted me with the secret of the magic playdough cookies. I got to help her make the real cookies and pull off the switcheroo, and I considered it of the utmost importance that my sister never find out the secret. Well a few years passed and she still believed it - she was reminiscing and I couldn’t stand taking part in this insidious lie anymore. I took her aside and broke the news. She was furious.