Israelis have great intelligence....

They can even distinguish types of tunnels...

Both Ahmeds are businessmen; they, too, have tunnels, through which they ship consumer goods like cigarettes and snacks, like the popular Egyptian potato chips called Chipsy and Crunchy, as well as larger products like generators, televisions and washing machines.

“It’s the No. 1 economy here,” Hillal Ahmed said. “Dollars, pounds, shekels, it all comes from the tunnels.” He laughed and opened his wallet. “We work for dollars,” he said, showing four neatly folded $100 bills.

But with the Israeli bombing, and, unspoken, the heavy Egyptian police and military presence that the crisis has meant for the town, the tunnel trade has stopped for now, the residents said. “Nothing is going in now,” said Nader Sayed, 28. “It’s impossible now.”

Hamas, the residents said, controls other tunnels, conduits for guns, cement, explosives and fertilizers for explosives.

Muhammad al-Zarb said that the Israelis somehow seemed to know which tunnels were commercial and which were run by Hamas, and that they seemed to be selective in their bombing. “If someone has a tunnel for Chipsy, it seems O.K.,” he said. “When a Hamas guy has a tunnel for weapons, they bomb it.”