A story from Perth, Australia sent along by a friend is comically instructional. Seems that someone stole a python from a wildlife center in Perth. The thieves no doubt thought they had made a clean job of it, but the snake did not cooperate. The six-foot long python swallowed a woylie, which turns out to be an endangered marsupial.
Turns out that the woylie had been fitted with a tracking device by the wildlife conservation department. So the police simply used the signals from that device to find the python with the woylie still inside. No doubt the crooks were shocked when the police stormed into the house where they were keeping the snake.