I just listened to the Darla scene through my system (M60's and SVS PB1 ISD), and in the closeup tapping part I heard two sounds. The most pronounced was the bass "doom, doom, doom" but at the start of each strike I think there was also another sound, like her fingernail hitting the glass, but not real sharp and somewhat obscured by the booming sound.
When the point of view changes, and the receptionist/assistant looks through the doorway at Darla, the sound becomes a very mild tapping from the external perspective, not the booming sound that the fish are hearing inside the tank.
I then took the DVD up to the bedroom, where we have a DVD player hooked up to a 20-year-old TV without any external amp or speakers. Without much of any bass capability, the "doom" sound was mostly gone, and the closeup of Darla tapping was more of a "doing, doing" sound, or maybe closer to the "tapping" that GaryG expected.
Boy it's hard to describe this without sounding ridiculous! I have to believe, though, that my Axiom/SVS delivered the sound that was intended, as so many others have expressed already. Perhaps it doesn't sound right if one hasn't heard the full effect before.
