Thick blood is not carried over from stage to stage, but serum is. The blood machine in each stage will cease to function if you revisit the stage, so learn to collect as much thick blood as possible in a stage and break the machine before moving on.

Unlock Hopper 7 mode by clearing Killer 8 mode. Hopper 7 only plays through the first stage.

Clear the game and unlock Killer 8 mode, where the changes include:
Enemy critical spots are invisible
Enemy explosions do five times normal damage
Clue and map icons are hidden on the map menu