Writing textbooks has got to be pretty tedious work. So you can hardly blame the writers when they slip in something that seems a little bit… off. My theory is that one of three things happens:
#1. The writer slips something in to see if anybody notices.
Best optometry chart ever.
The heading asks a very good question that the problem doesn’t really address.
Just don’t tell Spongebob he’s not a member. He’ll be crushed.
“This chapter might have been called ‘Introduction,’ but nobody reads the introduction and we wanted you to read this. We feel safe admitting this here, in the footnote, because nobody reads footnotes either.” Whoever wrote this is my hero.
This explains every other entry on this post.