Eeuw

Here's a sign from the student union (I paraphrase, from memory):  wanted, practice subjects to get paid to have their teeth cleaned at the college of dental assistanship science.  Must have pretty good teeth and (wait for it)--

Must not have had a cleaning for at least five years.

Two points:

• How can you have good teeth if you haven't had a cleaning for five years?  And

• Eeuw.