When the British captured senior German officers during WW2, they didn't put them in a prison camp. Instead they took them to a beautiful country mansion, and plied them with magnificent meals and drink, and allowed them to listen to German radio and read newspapers to keep up to date on the war. Each had his own room and a batman, and were treated like senior officers in the British Army.
Of course, the officers had much to talk about to each other, but unknown to them, the Brits had wired the entire mansion and had a team of intelligence officers working in the basement.
The intelligence they got was far more effective than pulling finger nails. They learnt a huge amount about the relationships between senior commanders and with Hitler. They also learnt a lot about German military strategy and tactics ... From the top.
Now that's intelligence.
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