If you’re prone to losing your wallet, keep it filled with cash. That’s a tip from researchers who “lost” over 17,000 wallets in 40 countries. In all but two countries, the likelihood of a stranger returning a wallet increased if there was money inside. And the more money in the wallet, the higher the rate of return, the researchers report June 20 in Science. Those wallet drop-offs were not without hiccups. Flooding in India rerouted the Swiss students, while authorities in Kenya detained one student for a few hours for appearing suspicious. All told, the students handed employees 17,303 wallets....