SEOUL — A brief yearly silence has once again enveloped South Korea, as half a million students across the country sit for the most important test of their lives.

Planes were grounded, construction work halted, and car honking discouraged as the Suneung, an eight-hour university placement exam billed as one of the toughest in the world, kicked off on Thursday.

But this year, there was one sound that students were especially scared of: "APT".

The global hit by Blackpink's Rosé and Bruno Mars emerged as a "forbidden" song among students who feared that its catchiness could cause them to lose focus during the test.

No distractions are too minor when it comes to the Suneung, which many see as a culmination of years of formal education — and a turning point that determines their university placements, careers, and social statuses.

"I’m worried that the song will play in my head even during the exam," one student told Yonhap News of the chart-topper. "Adults might laugh and say, 'Why stress over something like that?' But for us, with such an important test ahead, it can feel unsettling."

Suneung students have previously been encouraged to avoid other so-called earworms, with songs such as "Go Go" by BTS and "Ring Ding Dong" by SHINee repeatedly cited online as tracks that should be forbidden.

Ensuring that the exam runs smoothly is a nationwide effort. Shops and the stock market opened late on Thursday to reduce traffic congestion, and authorities adjusted public transport operating hours and put more than a dozen spare trains on standby in case of breakdowns.

More than 10,000 police officers were deployed, including some tasked to ferry students to school during emergencies.

Besides grounding planes to minimise noise disturbances during the 20-minute English listening test, authorities have also asked bus and taxi drivers to refrain from honking while the tests are taking place.

Disruptions to the Suneung are treated as a serious matter. Last December, dozens of students sued the government after teachers accidentally cut their test short by 90 seconds.

There are a record number of candidates retaking the exam this year, after authorities announced they would expand enrolment in medical schools — a move that was met with widespread protests among trainee doctors while being welcomed by aspiring medical students. — BBC