When you rub a glass rod against silk cloth, the glass rod becomes positively charged and the cloth becomes negatively charged. So they now can attract each other. However, after this 'attraction' takes place, the effect is lost after the objects neutralize or nullify each others' charges.
What happens when a comb rubbed against hair is brought near paper bits? Here, since the paper is neutral, I'm assuming the same 'nullification' of charge cannot quite take place.
Also, is this 'nullification' completely precise? Does the silk provide the exact number of electrons the (positive) glass rod requires?