In an early scene, a sign outside of the British pub in the story says it's The Gardeners Arms Pub, but later in the story Inspector Mulrooney calls it The Red Lion.
After Stephen Bannon cuts the ropes sealing the tomb; he holds the knife with his right hand. However in the next cut as he reaches down for the lamp; the knife is no longer in his hand.
Princess Ananka's mummy's death mask has closed eyes. In reality, the eyes of an ancient Egyptian mummy mask are wide open because the Egyptians wanted their dead to be able to see and hear in the afterlife.
There was no "Karnak" among Egypt's numerous deities. Karnak was a city, not a god.
Both in the outer and inner chambers of the tomb, there is far too much light but most especially in the inner chamber. The only light sources are the candle lanterns that Banning Sr. and Whemple are carrying but there seems to be light coming from multiple sources. The back wall of the inner chamber near the sarcophagus is literally bathed in light. In a real crypt such as the one shown, two candles would provide a very limited amount of light barely enough to see where one is walking.
When the mummy re-enters his coffin, he crosses his fore-arms. Crossed fore-arms in ancient Egypt was a sign of royalty and not for a priest.
When speaking at Ananka's entombing, Karnis speaks using King James English... 3,000 years too soon.
While Kharis is attempting to bring Princess Ananka back to life whilst reading from the Scroll of Life, Ananka's eyelids move. This shows that the spell was beginning to work.
When the mummy re-enters his coffin, he crosses his fore-arms. Crossed fore-arms in ancient Egypt was a sign of royalty and not for a priest. However some priests were indeed embalmed with the crossed arms - one example is owned by the Toledo (OH) Museum of Art.
When the archaeologists are breaking the seal on the tomb, the supposedly solid doors are visibly shaking.
In the scene where the mummy breaks through an upper window and into Stephen Banning's padded cell at the asylum, a large smudge of the swamp mud that covers the mummy suddenly appears on the cloth wall, even before Kharis slides down it, reflecting a prior take.
When Kharis is brought back to life as a mummy, he is in a standing position. In the flashback scenes, Kharis is shown to have been buried alive and, without food or water sealed in a wall crypt, he would almost certainly have collapsed before he died and thus should not have been standing when reanimated thousands of years later.
Mummy (an ancient Egyptian priest) understands commands from Isabel spoken to him in English.