It was very difficult. Harry and Seamus swished and flicked, but the feather they were supposed to be sending skywards just lay on the desktop. Seamus got so impatient that he prodded it with his wand and set fire to it – Harry had to put it out with his hat. In the books there are no explosion made by Seamus when his spell fails. Explosions are movie trademark. They put in for the comedy effect and to create a recognisable feature for Seamus as he isn’t that important in the films.