Researchers are tripping senior citizens on purpose, and it is not some kind of warped practical joke.
The goal is to prevent falls, which are the leading cause of injury in older people and cost 30 billion US dollars (£18 billion) a year to treat.
Conventional efforts include strengthening exercises, but researchers at the University of Illinois in Chicago are testing a different approach.
They started with a lab-built walkway that causes people to trip, as if stepping on a banana peel. Their research suggests that it helped build people's subconscious memory, teaching them how not to fall.
Next they will try computerised "tripping" treadmills that might someday be used in doctors' offices and clinics for fall prevention.
UIC professor Clive Pai called it a potential "vaccine against falls".