Each time you feed from someone, you forge a subtle link with them. This link is like an astral tentacle or a silver cord. It connects your subtle body to their subtle body. Every time you feed from this person after forging the initial link, you make this link stronger and deeper. The link can also be strengthened simply through casual contact with the person, so whenever you come together socially the link is reinforced bit by bit.
This link serves as a constant connection to the person. Through it, you can sense where they are, what their emotional state is, and if they are in any physical danger or distress. The deeper and stronger the link, the easier it is to travel down it in order to sense the person on the other end.
Through a strong link, you will be able to pick up stray thoughts in addition to emotions. You will also be able to implant suggestions and emotions. By tugging gently on the link with the person, you can make them think of you and draw them to you.
With concentration, an especially strong link will enable you to extend your awareness completely enough so your are able to perceive through the other person's senses.