"like a bad lobster in a dark cellar..."See in text(Stave One)
This simile depicts Marley's face on the knocker as having a kind of dull illumination. While we might not think that lobsters glow in the dark, seafood can contain luminescent bacteria that normally perish during the cooking process. However, if left to rot or decompose in a cellar over time, the bacteria can grow to the point where it would faintly glow.
"Hard and sharp as flint, from which no steel had ever struck out generous fire; secret, and self-contained, and solitary as an oyster..."See in text(Stave One)
These two similes define Scrooge in three ways: First, he is portrayed as inflexible through the comparison to flint (a hard gray rock). Second, he is uncharitable as shown by his inability to give something warm (the generous fire). Finally, he is not only isolated from others, but he also keeps to himself in his own world, contained within his own shell.
