Many of the older Oxford and Cambridge colleges have two doors in one doorway: the external one for the &#x27;interruptible&#x2F;not&#x27; signal, and the internal one to keep the heat in when the outer is open. We have a term for it: &#x27;sporting one&#x27;s oak&#x27;.<p><a href="http:&#x2F;&#x2F;www.grammarphobia.com&#x2F;blog&#x2F;2008&#x2F;02&#x2F;sporting-the-oak.html" rel="nofollow">http:&#x2F;&#x2F;www.grammarphobia.com&#x2F;blog&#x2F;2008&#x2F;02&#x2F;sporting-the-oak.h...</a><p>This was a great system in medieval buildings where most doors opened directly to the outdoors, which in itself is a great privacy feature.