Question: What exactly was O'Connell arrested and sentenced to death for?
Answer: Rick was purportedly sent to prison for deserting the French Foreign Legion. He was arrested after a bar fight, prompted by the pickpocketing of a certain Englishman.
Question: No matter how many times I watch this, I don't count all 10 plagues. Do some end up on the cutting room floor?
Answer: The plagues stop when they 'destroy' the mummy's powers. The good guys are trying to stop the mummy before the death of the first-born plauge (which they suceed in doing, as Jonathan survives the movie), as well as preventing the mummy from becoming all powerful and impossible to destroy - which would happen after the tenth plague. Some of the plagues, too, could have been happening while the good guys are in Hamunaptra and therefore not experiencing them themselves, bringing the total of plagues experienced by the outside world closer to nine.
Question: After the fire on the ship, and everyone gets out, Benny yells to O'Connell that he has all the horses. O'Connell yells back, "You're on the wrong side of the river." Benny makes a big stink about all that. My question is why? Surely it would not be so hard to cross a river.
Answer: Depends very much on the size of the river. The Nile at that point is pretty wide and deep, which doesn't make it particularly easy to cross. Benny and his cohorts would need to find a ferry or bridge to get across, which would take time. Even without horses, that gives O'Connell's group a considerable head start.
Question: At the end of the movie, as Rick, Evie, and Johnathon are leaving Humanatra, we see that Rick's bag is filled with gold from the city. How, where and when did Rick find the time to get some of the gold if him and his friends were fighting for their lives?
Answer: Beni (the bad guy serving the mummy who eventually gets killed by the bugs) can be seen carrying the gold out of the city. He then returns to get more, but can't get out any more. Rick and Evie just take the camel that Beni planned to use for the transport of his gold; they don't bring any gold out of the city themselves.
Question: The answer for another question made me wonder. If Imothep was alive when put in his sarcophagus, how can there be jars with his internal organs elsewhere? Wouldn't they still be in his body in order for him to be alive?
Answer: If you're referring to the only jars that are used in the movie, those are Anck Su Namun's organs. Not his. Near as I can tell, his organs were not taken, hence him being alive.
Question: I was chatting with my friends when I saw this film, and I think I missed an important bit. The Americans open something that brings a curse on them, yet O'Connell and company are the ones to open the actual sarcophagus. What are the Americans opening; and why does that bring on a curse, but not the revealing of the actual mummy?
Answer: According to ancient Egyptian tradition, four major organs (liver, intestines, stomach, lungs) were removed from the body during the mummification process and preserved in canopic jars that were buried with the deceased. The Americans found Anck Su Namun's jars whilst O'Connell and company found the sarcophagus in which Imhotep was buried alive. After Evie recites the curse that brings Imhotep to life, he needs these organs to bring Anck Su Namun back, leading him to hunt down those who are in possession of them. The opening of the sarcophagus doesn't actually invoke any curse and neither does the Americans opening the chest, contrary to what Beni says. The "curse" is only a warning that they shall become part of Imhotep's curse by taking the jars he needs.
Question: Why do they place a curse on Imhotep which makes his mummy evil? What would the Egyptians benefit from this?
Answer: It's ultimately a bit stupid, but a side-effect of the horrible punishment they've inflicted on him, making him suffer for so long, is that if ever he's resurrected he'll have powers and be immortal, which is why people are set to make sure he's never awakened. Just killing him would make more sense, but since when does anyone major die easily in films?