CCTV footage shows Wang Shichao, 77, lobbing the stick grenade into the driver's compartment of the bus in the district of Wucheng.
Fortunately, only the detonator went off -- with the explosives falling out of the device before any damage could be done. It caused a modest blast and a flurry of white smoke.
Jinhua resident Wang went on trial on Monday for allegedly causing the explosion on the bus last October.
Wang was quickly subdued by other passengers on the half-empty bus before police arrived at the scene and arrested him.
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During his trial at the Wucheng District People's Court, Wang said he was angry with the driver because he had not stopped precisely at the bus stop on a previous occasion.
Wang went home and dug out the grenade. He took it to the bus on an afternoon in October, the court heard, and attempted to detonate it next to the driver's seat.
Wang's attorney asked for leniency, citing Wang's age, poor health, that it was his first offence and the lack of causalities or loss of property.
The court would deliver its sentence at a later date.