Also, while AFAIK this is not from the shooting script, it's an earlier draft, here's Hooper's analysis as written down in the only script I could find online:
HOOPER
Left arm, head, shoulders, sternum
and portions of ribcage intact.
(to Brody)
Please don't smoke. With minor
post-mortem lacerations and abrasions.
Bite marks indicate typical non-
frenzy feeding pattern of large
squali, possibly carchaninus lonimanus,
or isurus glaucas. Gross tissue
loss and post-mortem erosion of bite
surfaces prevent detailed analysis;
however, teeth and jaws of the
attacking squali must be considered
above average for these waters.
If it was almost 30 seconds cut, this speech must have gotten longer. I can't tell if Brody is still holding the pack of cigarettes he pulled the one out of when we cut back and Hooper says "indicates", if he isn't there had to be enough time for that bit of business.
I also found this old forum post on The Straight Dope of someone with his own take:
"I think the reason is simple. That exact bit, with lifting the arm, was an effects shot and was filmed months after principle photography. It's probably not the same set and definitely not Richard Dreyfuss lifting the arm. Consequently Dreyfuss' line was looped (i.e. recorded & added in later). And in this case, added in rather badly (this was the 70s). The acoustics of the added line's audio don't match the rest of the scene at all."
In the Bryan Singer interview Spielberg makes it seem like the arm insert was pulled from elsewhere in the scene, but maybe it was indeed a pickup done after principal? We don't see Dreyfuss' face, we only see a bit of the room (even if it looks like everything matches up), so maybe they did just rebuild a small part of the set, bring in Scheider but use a body double for Dreyfuss. An alternate possibility is that what was cut was actually much shorter than Spielberg remembers (i.e., "Do not smoke in here, thank you very much!", and says that something "indicates the non-frenzied feeding..." as Brody complies with Hooper's request and puts the cigarette down - if it was 30 seconds like Spielberg recalled to Singer, that'd be a long delay between Hooper telling Brody not to smoke, and Brody taking the cigarette out), and the arm insert was a later pickup to *add* some extra oomph to the scene and make it a bit less clinical. Maybe in the original version as shot during principal we didn't even see the arm.
The point is that whatever it is, it is undoubtedly much more mundane than the removal of some mythical extra graphic footage, and the arm shot was either cut in from a different angle shot during principal, or was completely invented during pickups, to cover up an edit in the middle of the continuous take of Hooper's speech -- and "This is what happens" was either dubbed in from another part of the scene, from a different scene entirely, or was recorded during post so there would be something that could conceivably lead into "--indicates the non-frenzied feeding" now that the original beginning of that sentence was excised.
