After news leaked that US medical-device maker Stryker was working on a bid for UK rival Smith & Nephew, the body here that regulates mergers and acquisitions told the American company it had 28 days to make a binding offer, or walk away for six months. Stryker walked away.

Stryker-whose six-month lockout ends this week-is one of several companies that have had plans for large acquisitions thwarted by the rule known as "Put Up or Shut Up."