In the autumn of 2023, Wojciech Brylinski was analysing data from the NA61/SHINE collaboration at CERN for his thesis, when he noticed an unexpected anomaly – a strikingly large imbalance between charged and neutral kaons in argon–scandium collisions. Instead of producing roughly equal numbers, he found that charged kaons were produced 18.4% more often. This suggested that the “isospin symmetry” between up (u) and down (d) quarks might be broken by more than expected due to the differences in their electric charges and masses – a discrepancy that existing theoretical models would struggle to explain. Known sources of isospin asymmetry only predict deviations of a few percent.