BAGHDAD (AP) – Two mentally retarded women strapped with remote-control explosives—and possibly used as unwitting suicide bombers—brought carnage Friday to two pet bazaars, killing at 73 people in the deadliest day since Washington flooded the capital with extra troops last spring. The coordinated blasts—coming 20 minutes apart in different parts of the city—appeared to reinforce U.S. claims al-Qaida in Iraq may be increasingly desperate and running short of able-bodied men willing or available for such missions. But they also served as a reminder that Iraqi insurgents are constantly shifting their strategies in attempts to unravel recent security gains around the country. Women have been used in ever greater frequency in suicide attacks.