DHAKA, Bangladesh (AP) -- Police say they have rescued two spider monkeys who had been trained to sell contraband drugs by recognizing the colors of different currency.

The monkeys were found in chains when police raided a house in a Dhaka residential district July 4, seizing 40 bottles of phensidyl, a narcotic syrup, and arresting three men, officer Imamul Hossain Feroz said Monday.

When addicts entered the house, the monkeys met them, he said. If a visitor handed cash to the female, Munni, then Hamid, the male, would get the drugs from the roof, from under the bed or from another hiding place.

Munni handled only 50- or 100-taka paper notes, and was trained to tell the difference by their color, Feroz said. A 100-taka note is black and white and a 50-taka note is red.

The monkeys were also trained to understand some hand signals, he said.

The house was raided on a tip from neighbors, and the monkeys were taken to the National Zoo, he said. The occupants, charged with drug possession and dealing, face the death penalty if convicted.