As you start out the lesson let the girls know that you prepared cookies for them and pass them out. Pass out the second batch of cookies, the ones in which you did not measure the ingredients. See if you get any reactions. If they are too polite to say anything you can let them know that there is something unusual about these cookies. After they point it out say that you can’t understand what went wrong, you threw the indredients on the list but that you didn’t think it was very important to measure them. Then give the girls the real cookies and tell them you followed all the instructions on this batch. Have them tell you what they think.