Tessellate

Tessellate, while it means the fitting of identical shapes, also is the fitting of pieces in a plane that have no overlap and no spaces. If think about the heart in a plane sense, there is only the outer edge, there are no lines running through the middle cutting it into concise shapes. But when it is broken, the pieces fit together perfectly, but now they are forever their own pieces, no longer a union.
This idea, coupled with the line, "dead lovers salivate" are meant to be sort of ironic statements. A heart is never the same after it's broken, and a lover can no longer "salivate" or desire who they did in their physical life. In general the song is talking about how when things happen, there will always be change, and it will always be noticeable, whether in the pieces of a heart, or in how someone no longer "salivates" for you. This ties into the verses, in the boys who get the nerve to tell off their overbearing mothers, or how the poor cannot overcome.