So my mom always tells me that whenever I'm standing looking at something, sizing it up, I slant my head a bit. Especially when I'm getting ready and looking at myself in the mirror (I've noticed my cat does this as well, so what does that mean?). Anyway, while I was looking at this photo, I realized I had tilted my head a bit and thought of this other picture taken of me while I was 4 years old and in the utopia that is a Disney cruise.
So I guess for me, the similarity comes from a family joke. But also, I really do own slanted bookshelves.
(bookshelf image by Melchior Tersen / found via)