In the episode when Cell returns to Earth after self destructing on King Kai's planet, Cell uses one of Frieza's finishing moves to kill trunks. When trunks is hit by the attack all of the Z fighters(including Vegeta) turn around and gasp in shock as they see the newly slain Trunks. Cell begins talking so they all turn to face him and listen, soon after Gohan powers up to fight Cell. Just as Gohan is about to attack Vegeta catches a glimpse of something in the corner of his eye and turns around to discover for the SECOND time that Trunks is dead, and then of course he is ticked off. How many times does he have to see his dead son in order for it to sink in? Also another slip-up with this scene is the color frieza's finishing move that Cell uses on Trunks. When Cell was using the same attack on Gohan to make him him angry, the attack was colored pink, and just a short while later when he uses it on Trunks it is yellow.