So I was searching the Internet Archive for other old videos that might have LucasArts game stuff in them, and I found a
video covering the 1993 CES expo.
Among the attractions shown was LucasArts' booth, where
Day of the Tentacle was being previewed.
The computer with DOTT. There's an odd inventory icon just visible: it's the human anatomy chart Laverne finds in Dr. Tentacle's office, which can't be picked up in the final game.
The same point in the game, and same extraneous chart, seen in a scan from
Adventurer #5.
The DOTT intro. The bird in the foreground is grinning stupidly at the camera, an animation not used in the final game.
The bird, overcome by the pollution of the Sludge-O-Matic, collapses and dies.
Notice the right side of the screen, with the fungus-encrusted tree and bird nest. That part of the background was removed in the finished game, and the bird's death animation plays out farther to the left.
The Internet Archive also has some DVD-quality versions of the video: I downloaded them and took screenshots, but haven't posted them here out of courtesy for dial-up users.