TWO housemates were arguing about unpaid rent and a missing dog when one fatally stabbed the other in the heart with a pocketknife, a Perth court has heard. Craig Stephen Sewell, 25, is on trial in the West Australian Supreme Court charged with the murder of Adam Ross Sellin, 36, in March last year. Prosecutor James Mactaggart said in his opening address today that the men were arguing about rent money Sewell and his girlfriend owed Mr Sellin for their room, when the exchange developed into a scuffle. Sewell suffered a black eye and bloodied nose from the fight after Mr Sellin repeatedly punched him in the face, and Mr Sellin was also injured, Mr Mactaggart said. Mr Sellin told Sewell he had to move out, so he and his girlfriend walked to a neighbouring house where her uncle lived, he said. Mr Sellin joined a friend in a ute and began looking for his dog, which had gone missing, when they spotted the couple, Mr Mactaggart told the court. Unarmed, Mr Sellin got out of the ute and demanded they tell him if they knew anything about the dog, he said. A scuffle then ensued, and Sewell produced a knife and stabbed Mr Sellin in the heart before running away and dropping the knife in a drain, he told the court. But defence lawyer Tom Percy said it was a "classic case of self-defence" after Mr Sellin came ``menacingly" towards Sewell and his girlfriend. He said the couple were "minding their own business" in her uncle's driveway and waiting for a taxi when a drug and alcohol-affected Mr Sellin ran towards them. Mr Percy said Sewell feared for his and his girlfriend's safety, and produced the knife as a "last resort" to defend himself, stabbing Mr Sellin in what he thought was his stomach. He said Sewell last saw Mr Sellin staggering to his friend's ute and said he dumped the knife because he panicked. The trial continues.