The pull up call comes from the Ground Proximity Warning System, the automated cockpit alert that warns pilots of dangerously low terrain, which became standard in airliners like the DC-9 in the 1970s. The McDonnell Douglas DC-9 itself was a 1960s short-haul twinjet, and its older warning voice has a distinctly dated synthetic sound. Clips of the alert spread through cockpit videos, air crash documentaries and flight simulator communities, and editors still use it because two words instantly signal aviation danger to any audience.