answer:I have always used guillotine clippers but it doesn’t really matter as long as they are reasonably sharp. Often the end of the nail beyond where the blood vein reaches is brittle and powdery, that is probably what cracked. The vital part of the nail should not crack. If you look at the end of the nail if it is still white and powdery like you are fine and can go a little further, if it looks pinkish and like flesh then you have gone far enough. If you do go too far and it bleeds, any powder will help it to coagulate, talcum powder, pepper which is a natural coagulant. No biggie really!