Just an observation really and something that i haven't seen brought up, when lisbon enters the house (whos house is it??) there are signs on the wall in red (possibly blood) that say "DIE" "666" and a pentagram?? 
Now they may not be significant and i can't really think of any theories for the symbols other than its religious? and the poem tyger has been analysed as a religious poem. 
Sounds weak i know... just wondered if anyone had any thoughts??