Find the Hammer Bros. attacking from brick platforms in World 5-2 or 8-3, then stand next to the pit behind them. Have small Mario follow a hammer down the pit, and you'll hear the "lost a life" sound interrupt itself and play a second time if Mario hits a hammer after falling off-screen. Though the "lost a life" sound plays twice, Mario only loses one life.

This is possible because when Mario falls down a pit, he actually keeps falling until the black "World x-x" screen appears. If Mario collides with a hammer during his free fall, he stops falling and performs his standard death animation off-screen.