Audio problem: Near the end of the movie, when the police break through a skylight, you can hear the glass break at the skylight, but when the glass reaches the floor there is no sound of the broken glass hitting the floor. (01:24:14)
Audio problem: On the Silicon Graphics computers, one of the sound effects heard is a floppy disk drive access sound from an Apple Macintosh computer.
Answer: More then likely, the dog was too afraid of the Kothoga to attack it and when the Kothoga saw this, it let the dog live. The other dog was probably unafraid and tried to attack the Kothoga which prompted it to kill the dog; not out of self-defense, but, because there were still people trapped in the museum and the dog was impeding his attack.