I read a newspaper article a few years ago about the opening of a KGB museum in Russia. According to the article, they finally revealed why American spies were so quickly arrested in the former Soviet Union. It seems that the Soviets used ordinary steel staples in their passports and other documents. These staples quickly rusted. American staples were made of galvanized steel and didn't rust. So, all it took was for someone to demand to see the agent's papers (a very regular happening). If there was no rust, they were arrested. At least, that's what the article claimed.

Attention to detail - lack of on the CIA's part.