Facebook...

always presents one with a box preceded by a seriously annoying prompt:

What's on your mind?

There are so many things wrong with this question, existentially, ontologically, epistemologically, and neurochemically, that even to proclaim the obvious answer that it has to be cerebrospinal fluid combined with vague and traumatic memories of cereal commercials from early childhood, and possibly a diversity of amyloid plaques, fails tragically to divert attention from my inability to enumerate them.