Yui: Mommy, here’s my new character. She’s always happy. But when somebody does bad, she releases poison at the speed of Mach 10.

Me: you know what Mach is?!? You know how fast Mach 10 is?!?!

Yui: yes. It’s so fast you can’t see it.

She’s barely 9. I won’t even share how old I was when I learned about Mach.