The Great Divorce, Chapter 11, what about the Ghost with the lizard on his shoulder at the end of chapter 11; what is Lewis saying about the nature of lust/desire in this story?

In Chapter Eleven, Lewis contrasts and compares two kinds of love (counterfeit love), these examples include lust and selfish love. Lust is symbolized by the ghost, who has a lizard on his shoulder. The lizard (lust) had to be killed before the ghost could make progress, because there is no place for lust in a perfected character. The angel insistents the lizard (lust) must be killed, but the angel cannot kill it without permission (the ghost's prmission). When the ghost agrees to give up the lizard, his transformation is immediate and stunning.