Having been a twin, I can say that twins can always make a long list of how they differ. That list comes from lots of comparing and often involves things that no one else would notice. Also, the complete list of differences always includes things that life has done differently to the twins. My brother had an encounter with barbed wire when we were young. The scar through his left eyebrow was so obvious to us, but no one other than relatives spotted it. He ended up smoking and weighing more than 80 pounds more than me. I'm still living twenty years after he died of lung cancer. That's a difference I am happy about, but I miss him greatly.
Now, when we were younger, we matched. We shared a bedroom and a bathroom which didn't have a door. So, I saw 21 years of him growing up and vice versa. We knew each other from cow lick to toe jam. After that, when we got together, we always shared info about our bodies. I had to be circed and he underwent the procedure just to match me.
Once at a Mardi Gras event, we shared a hotel room with our girlfriends. In the middle of sex, we switched partners. Neither girl knew.
Parents, teachers, coaches, etc couldn't tell us apart. So, we answered to "Hey twin" more than our names. Once switched jerseys at half time in a basketball game because I was a hot shooter and a bad fouler. With the switched jersey, his stats really improved in the second half. No one ever knew.
Once took an accounting final for him in college. Teacher required a driver's license for an ID. We swapped them before the test. Got him an A.