CADEREYTA JIMENEZ, Mexico >> Couples were walking hand in hand. Children were frolicking. Just down the road in this northern Mexican town, 49 bodies, headless with their hands and feet severed off, had been found and cleared away.Francisco Umberta, alarmed by the latest in a string of unimaginably gory crimes linked to Mexico’s drug war, dealt with it by heading out on a date. A half-hour drive from where the torsos were discovered, he stood in line Monday near a crowded Chili’s restaurant to buy movie tickets for “The Avengers.”“Of course it is all scary,” he said of the massacre, which sadly set no record for carnage here, “but what are you going to do?”He had heard about the bodies on the radio shortly after they were discovered Sunday but said the regional soccer playoffs drew more public attention.“It’s not like we’re all paralyzed,” said Umberta, 31, an office clerk. “We still need to live while they do what they do.”With mangled corpses turning up on street corners and inside restaurants, hung from bridges, and buried in mass graves, Mexicans seem to have grown inured. Outrage, fear, anxiety, sadness — it is tough to muster such emotions again and again, especially with 50,000 people dead in drug-related killings since President Felipe Calderon began his assault on traffickers six years ago.Other countries, of course, have gone through some version of this collective numbing: Israel in 2003, after a series of bus bombings; Iraq in 2006.But Mexico seems to have fallen to new depths of deliberate distraction this year, and many Mexicans are increasingly disturbed by their own attitude. They are equally depressed about its cause. After all, crime experts and psychologists say, the apathy — during a presidential campaign, no less — is really just a learned response to repeated trauma, and impotence in the face of horror.Mexicans in city after city have grown used to death tolls that climb continuously. Protests, marches and public art projects honoring the many victims have done little to alter reality. Every day, families and children walk by newsstands with tabloids showing graphic photographs of the latest corpses to be found. Most barely notice.“We know nothing is changing — it just goes on,” said Imelda Santos, 17, who was out enjoying a fast-food hamburger with friends. “We try not to worry too much because we are not involved.”That perception — it’s them, not us — appears to play a large role in people’s ability to remain disaffected despite the carnage.“For a lot of Mexicans, the big impulse is ‘Well, that’s just too bad, but at least we got rid of the bad guys,”’ said Jorge Castaneda, a former presidential candidate. “That contributes to the jadedness.”In the case of the 49, perhaps some were on the wrong side of the law. The authorities have said several had tattoos of Santa Muerte, the unofficial saint of death often favored by cartel assassins.Mexico’s interior secretary, Alejandro Poire, said Monday that the Zetas, a drug gang known for its ruthlessness in a country known for it, too, appeared to be responsible for the killings. Security experts have surmised that the high-profile dumping was a response to mass killings by the Sinaloa cartel.The two groups are Mexico’s most powerful criminal competitors. They are also regional and cultural opposites. Sinaloa has been moving drugs north from the ranch country of western Mexico for generations; the Zetas are newer arrivals, founded by former special forces soldiers who had been enforcers for the Gulf cartel on Mexico’s more urban eastern coast.They are battling each other, invading each other’s territory and leaving behind bodies to intimidate their rival. The latest wave of violence seems to have started, or intensified, in September when a group identifying itself as the Zetas Killers dumped 35 bodies on a highway at rush hour near a mall in the Gulf Coast city of Veracruz.Two months later, 26 bound and gagged bodies appeared in downtown Guadalajara, a Sinaloa stronghold. Then, on May 4, 23 people were found dead in the Zetas’ border state of Tamaulipas. Fourteen were decapitated. Nine were hanging from a bridge.“This is tit for tat,” said Alejandro Hope, a former senior intelligence officer. “For Sinaloa, it’s a way of bringing down these upstarts, and for the Zetas, it’s about protecting their reputation for extreme violence, which is their main asset.”Even though tit for tat makes sense in the latest massacre, experts say the explanation may turn out to be something else entirely. The victims, who included six women, might have been innocent migrants, like the 72 Central Americans the Zetas are believed to have killed and dumped in a grave discovered in 2010, or the 193 bodies found last year in another set of graves in Zetas territory near the Texas border.Given the violence, psychologists say it is no wonder people are checking out.“One strategy we use for protection, for survival, is to ignore it because there is nothing we can do,” said Maria Antonia Padilla Vargas, coordinator of a nonprofit psychological research group. “It’s a phenomenon we’ve observed when rats are exposed to uncontrollable electric shocks.”The official term is “learned helplessness,” and case studies are appearing all over Mexico. In January, two headless bodies showed up in a smoldering van outside a fancy mall in the Mexico City neighborhood of Santa Fe. As the police tape flapped in the wind, Carlos Alberto Govea, 24, kissed his girlfriend a short stroll away.Residents of another neighborhood in the capital, where a shootout last week killed six people, said they had already stopped discussing the crime.“It’s better to leave these things in oblivion,” said Andres Castillo, 68, eating a tamale near a shoeshine stand. “We are coming to terms with the idea that we may leave our houses and not come back.”Even in Ciudad Juarez, where violence is declining but still at a high level (two heads and four hands were found in a bar’s parking lot Monday), residents are determined to avoid seeing the tragedies in their midst. When the families of missing or slain girls gathered outside the state prosecutor’s office to protest what they consider the authorities’ lack of interest in their cases Thursday, Mexican Mother’s Day, drivers cruised by without looking.And the three main candidates running for president? They have kept their distance, too. With Calderon constitutionally barred from running again, all the campaigns have largely focused on other things. Many Mexicans doubt that whoever wins will create immediate change, and turnout for the July 1 election is expected to be light.“The politicians have not been able to resolve this,” said Jose Juan Cervantes, a crime and sociology researcher at the Autonomous University of Nuevo Leon. “So the people cope.”Indeed, here in Cadereyta Jimenez, the streets were full Tuesday as Edelmiro Cantu campaigned for mayor. He heard often about voters’ preoccupation with security, but even he did not seem convinced that the government could solve Mexico’s crime problem. So instead he carried his own protection.“I have this,” he said.From his pocket he pulled a small silver crucifix.