3. Why is this xkcd cartoon (552) funny? 
The cartoon is about the maxim “correlation does not imply causation.” In the third panel, the left speaker tries to attribute causality to the statistics class, but the right speaker correctly shrugs it off. That reminds me that Katherine and E.B. White wrote, “Humor can be dissected, as a frog can, but the thing dies in the process and the innards are discouraging to any but the purely scientific mind.”
I awarded bonus marks to anyone who worked the Latin expression “post hoc ergo propter hoc” into their explanation. Nothing makes a dissected frog funnier than writing the labels in Latin.