if(t==PT_SPRK&&parts[i].ctype==PT_ETRD&&parts[i].life==1)
{
nearp = nearest_part(i, PT_ETRD);
if(nearp!=-1)
{
create_line((int)parts[i].x, (int)parts[i].y, (int)parts[nearp].x, (int)parts[nearp].y, 0, PT_PLSM);
t = parts[i].type = PT_ETRD;
parts[i].ctype = PT_NONE;
parts[i].life = 20;
parts[nearp].type = PT_SPRK;
parts[nearp].life = 9;
parts[nearp].ctype = PT_ETRD;
}
}


in powder.c


EDIT: Replace the PT_PLSM with PT_THDR to send thunder