I thought this was a gentle exposition of the difference between "lay" and "lie". Basically,
The main difference between the two words is that lay is a transitive verb, while lie is an intransitive verb.
|Verb||Infinitive||Past Tense||Past Participle|
The summary is the best part, emphasizing the lesson.
So here's the drill:
You need to lie down today, yesterday you lay down, in the past you have lain down.
Today, you lay the book on the table. Yesterday, you laid the book on the table. In the past, you have laid the book on the table.
Update: Of course there's an XKCD for that: Fashion Police and Grammar Police. This comic describes my grandparents: one set sold clothing, the other set were sticklers for the proper use of the English language.