I guess you don;t really break the metaphor, well you do, but then you go back into it. I just think it would be more interesting if it was subtle the whole way through. If you keep up the illusion of Jack being a human companion on a trip it is less trite and clichéd. Thats why the verses work so well.
The second verse is real good to. Like I said it is much more interesting when it's not obvious, better imagery and all. The refrain just needs a little tweaking.