they were even dumber than thought.

The thing was attracted to the light.

It's shown when it walked right by them at the end, when the lights were off. It did not see them. Also, at one point Dr. Miles says to turn off the light, and that worked (but they forgot it later)

Zahir was killed because he had a light with him, which gave away his location to anubis.

At the end when anubis follows them up the shaft, the light was on the whole time.

However don't be too judgmental because most of you would probably have pissed your pants in their situation.

I believe anubis didn't eat Dr. Nora's heart because it thought she was pure of heart, but realized it didn't want to ascend to heaven to join osiris anymore (although, the veracity of this is thrown into question as in the beginning, it's shown she was motivated by fame).

The egyptians at the site had found another entrance but didn't tell the archeologists. When Dr. Nora goes through it, anubis follows her out of the exit into the world.