Dreads will try to merge with the ones around them if you aren't careful! It can happen down the body of the dread with just a little loose hair, or at untended roots. In either case, you can separate them by pulling the individual locks apart, down to the scalp. This will totally hurt - so try to be as gentle as possible! If you are very VERY careful, and you can see exactly where the hair is joined, you can make a small cut to help get the separation going.
To prevent them growing together in the first place, keep up a consistent palmrolling schedule, and run your fingers through your dreads every day. Snapping one or two hairs is better than trying to rip through a whole section. Trust us.