I have a hard time keeping basil.  When I buy it from a local grocery store, it is perfectly fresh, but when I take it home it withers in a couple of days.  I have tried keeping it in fresh water and trimming the stems, but that only extends its life about 48 hours. My current record is 3 days before it goes bad, and I only got that by trimming and replacing water every 16 hours.  What is the secret here? How can I keep the basil alive? 
All cutting (slicing, chopping) knives should be as sharp as you can get them, really. A dull knife is much more likely to cause an accident and cut you. Dull knives are more difficult to use properly and any knife used improperly is likely to lead to accidents. The duller the knife the more pressure you need to apply in order to cut your food, leading to a higher chance of slipping and hurting yourself 