Don’t forget the “obligatory” double.

Do you play "Negative Doubles"?  If the answer is yes 
then you have to remember that you also play "obligatory"
doubles.  Let's assume that you open one spade and your 
left hand opponent bids two hearts. Your partner passes 
as does your right hand opponent.  You now need to look 
at your hand and evaluate the possibility that your partner 
would have liked to make a penalty double but could not 
because it would have been a negative double.  If you have
a decent opener and shortness in the suit that was overcalled,
you should re-open with a double.  If partner wanted to make
a penalty double he will pass, and if he did not he will make
a bid to let you know that he does not have that hand.