Originally posted by the Dark Marauder
The "two hands needed" thing is the canopic chest where Imhotep's vital organs are stored. Placing one hand on the chest activates the rumbling/evil inside. Having two hands on it summons the power of the Med-Jai to calm the evil/protect the visitors. Not everyone reads the instructions, though.
As for the "blue light thing", that's a scarab, and the mirror shows those that have gone ahead of you. Placing your hand on the scarab when it is blue will send a blast of ancient air to whomever is on the bridge, which sometimes results in a scare. A translation there might help.
Also, a lot of people only look at the key to the book of Amun-Re in Imhotep's burial chamber. Some do try and grab it, which triggers the effect.