What dangers do migrants confront boarding the trains?

Enrique considers where he should hide on the train. The boxcars are dangerous, as there is little to hold on to, but la migra does not normally go up there. Inside the boxcars is worse. He could be trapped inside for days, without food or water, and die of heat exhaustion. He could hide under the cars, between the axles, but he has grown too big to fit safely. Enrique decides to settle in on top of the hopper car, and holds on for dear life. He is afraid his car will tip over. There are also the dangers of Madrinas. They are men who wear civilian clothing but help the authorities capture migrants.