I suck in my cheeks when I concentrate. I have ever since I was a small child. The harder I'm concentrating, the more my face resembles that of a fish. It's embarrassing, especially when a photo of me concentrating hard on a quilt, cheeks sucked in and brow furrowed, is featured in a Stake Women's Conference slideshow like it was last Saturday. :) I don't realize I am even doing it, which makes it a hard habit to break. Luckily Sam thinks it's adorable (how does he think all of my weirdo quirks are cute?!?), so it's not really a problem.
Talmage doesn't suck in his cheeks when he's concentrating, but he gets very into the task at hand. For example: