he held the twist far out over the side , two of his mates holding his waist to keep him steady while he unwound the twist and carefully spilled the yellow powder into the case , watching with only one eye , the other squinted up and his face half-turned away ; his cheek was spotted with black scars , reminders of previous work with the powder : it needed no fuse and would go off on any careless impact , burning far hotter than gunpowder , if spent more quickly .