I'll give you a couple twin stories. My boys are 10 now, but these happened when they were 5 and 6.
I was busy with my older son's school's auction. I had hubby doing the bedtime routine with the twins. When I got in I went up to give them a hug and kiss, and Twin B's hair was matted (I had given them a bath earlier that day). It was blood. He had bonked his head on the cabinet door and got a good cut.
The next day while driving them to school, I asked why they didn't tell dad about Twin B's cut.
Twin A: We were waiting for it to heal.
Me: Guys, you need to let mom and dad know so we can clean up the injury and it will heal quicker.
Twin B: You said you could see my brain, Guy!
Twin A: Guy, guy, I was kidding.
Twin B: No, Guy, you saw my brain.
Me: Twin B, he didn't see your brain. And if he could see your brain it would be very important to tell mom and dad.
Second Story:
At an open house when the boys were in Kindergarten a little boy came up to me and, pointing to the twins, said "They're brothers."
I responded with "Yes." He then says "They're twins."
Before I could say anything Twin B yells "Stop calling us that!"
I read up on twins to the point of overkill. One thing I kept reading was that they should have their own identity. So I never called them twins, in front of them, anyway. Poor Twin B, thought the kid was calling them names, LOL.