The killing hand -> After the line "I laugh at what I've done" JP makes a laughing sound with his guitar
The ones who help to set the sun + A nightmare to remember -> According to JP on the WDADRU dvd (if you rememeber it right), TOWHTSTS is about a guy who's driving in the middle of the night and somehow slips into a flashforward of his own death in a car crash then comes back to reality, having a sort of a revelation... A nightmare to remember's subject matter is somehow similar to that - both songs begin with thunder soudn effects.
Voices -> around 4:52 you can hear the main erotomania chromatic riff reprised with keyboards.
Erotomania -> one of the cool things i like about DT is that they take different musical sections and shapeshift them therought different time signatures; after JP's final solo in Erotomania, there's heavy section which goes in bars of 4/4 and finally a bar of 3/4 , before reprising the main riff of the song - through the heavy section, the main riff is being played by Kevin's synth sound, only that it's being played in 19/16 (10/16+9/16) loops! And each time thge 4/4 bar starts, we hear the synth melody start off on a different melody. In other words, 4*(4/4) + 1*(3/4) = 64/16+12/16=76/16 , and 4*(19/16) = 76/16 ; that's why they end up matching
Octavarium -> After the "Full circle lyrics" (Find I've come full circle) The instrumental section begins, in a diminished scale movement -
Now you know the diminished scales have this loop (full circle) effect; that every 1.5 intervals they repeat each others - for example, E diminished (E-F#-G-A-A#-C-C#-D#-E) has the same set of melodies as G diminished (EG-A-A#-C-C#-D#-E-F#-G)