Asia watchers are used to watching neighbours Singapore and Malaysia lightheartedly lob insults at each other over the provenance of their joint cuisine. But the Southeast Asian countries ended 2018 with a far more sombre dispute than their decades-old food fight - one that has continued into the new year.
The row over airspace and maritime boundaries has given rise to jingoism on both sides, and observers say the bilateral relationship is currently at its worst state in two decades.
The downturn comes after veteran politician Mahathir Mohamad, 93, returned as prime minister last May after an election in which his scandal-haunted predecessor and one-time protege Najib Razak was roundly trounced. Just last January, ahead of the polls, Najib had declared that the "confrontational diplomacy" between the neighbours that marked Mahathir's first stint in power from 1981 to 2003 was firmly in the past. He spoke too soon.
This Week in Asia takes you over the main sticking points in the relationship between the neighbours.