We've been having some trouble remembering which common words take an "h" after the "w" and which do not. This morning, we cracked the case. Among the most commonly used words, those that ask investigative questions begin with "wh." Of course, because Watson and Holmes are there to investigate.
Who stole the diamonds.
Watson and
Holmes want to know
why? And
when?
Which way did he go? And
where?

There, Watson, this infernal case has haunted me for ten days. I hereby banish it completely from my presence.
--Sherlock Holmes