I get those. My impression is that they come about because my hair sometimes climbs itself as it curls, and can actually tie itself into a knot that way. It seems to help to try to finger comb my hair particularly well when I have my conditioning conditioner on it. When I get them, though, I have to cut them off (with hair shears, so the scissors don't shred the hair), or it just becomes worse, and can draw other hairs into a tangle.
Peace,
Morgan

Baby Fine 3B, low porosity, normal density and elasticity
CGing since July 2008