For those of you who have children who use sippy cups:
If, hypothetically, you were to take your children to the store for a quick trip and they were to say, throw their sippy cup overboard from the cart, you might want to check to make sure the valve (the one inside to prevent leaks) is still intact and in the proper position before putting it in your purse.
Otherwise, you run the risk of foreign substances invading your purse. Like apple juice. It might even leak out of the purse and run down your leg. Apple juice is sticky.
And you might be very thankful that you have a cloth, washable purse. And that you decided to put your cell phone in a place out of the way of the torrential leakage.