At 4:05, when Mitchell checks the DHD, you can clearly see the symbol for earth. This seems not possible as the point of origin symbol is unique on each Stargate and DHD. However, the symbol for Earth is used as a point of origin only if dialing from Earth; on another planet, it could be used as part of the six gate address in order to travel to a totally different planet. Claiming that the Earth symbol should not be on other DHDs is analogous to claiming that the E symbol should not be as the longitude co-ordinates of maps if used somewhere in the east.
As the opening scene is fading to intro, Vala can be seen speaking, though her audio cannot be heard.