An elastic band (or rubber band if youl will) can expand > grow And likewise an elastic band can contract - that's what they do. So the "I" of the song probably feels both hate and love for this other person. In the song she compares herself to a rubber band, when you pull to hard, the rubber band will snap and so will she. Snap meaning several tihings - breaking, breaking down, up and into two. But she has got thick skin - her rubber band is strong. It bounces back. This sounds like an unhealthy on/off relationship. The rubber band expands and contracts (just like a beating heart) in what sounds like an ongoing and neverending cycle . The rubber band reminds me somewhat of a boomerang in this song - it always return. She is possibly not likely to break the cycle. - Because you cannot conquer love.