Identical twins don't have identical DNA

I studied Biology in college and loved genetics. However, there are constantly new studies being done.  I learned something new this week all because my students got into a debate of whether identical twins truly have the same DNA. Some said yes, some said no. Both sides had a great reasons to back themselves up. What were the results of the research? Well, scientists knew that identical twins could express genes differently but their studies showed while they have VERY similar DNA, they don't have the exact same DNA. Identical twin don't have identical DNA. Being a teacher means I get to constantly keep learning. :)  I have also wondered why identical twins didn't look exactly identical. I knew there were facts that turned some genes on and some off, but I didn't know they could actually have some differences in their DNA. God is such an awesome designer!