CARACAS - (AP) -- Venezuelan President Hugo Chávez called his Mexican counterpart a ''puppy of the empire'' for supporting a Washington-backed free-trade zone at the Summit of the Americas. Mexico reacted by calling in the Venezuelan ambassador, Vladimir Villegas Poljak, to explain Chávez's remarks. ''How sad that the president of a great country like Mexico allowed himself to be the puppy of the empire,'' Chávez said Wednesday evening in his first public speech since returning from the 34-nation summit in Argentina. The barb comes after Mexican President Vicente Fox, apparently irked by Chávez's strident calls against the trade pact, said...