Dubai: What began as a suspected food poisoning case linked to a late-night watermelon has turned into one of Mumbai’s most disturbing mystery deaths — with forensic investigators now tracing the deaths of a family of four to rat poison. Authorities say traces of zinc phosphide, a highly toxic rodenticide commonly used as rat poison, were found in both the watermelon consumed by the family and in viscera samples taken from the victims, sharply shifting the investigation from contamination fears to a poisoning probe. The victims — a couple and their two daughters — died within hours after falling violently ill at their home in Mumbai’s Pydhonie area. According to initial police findings reported by The Indian Express, the family had hosted relatives for dinner before later eating watermelon around 1am. By morning, all four had developed severe vomiting and rapidly deteriorating health. None of the dinner guests, who did not eat the watermelon, reported symptoms.…