Got this little tidbit from the local Democratic party. For those of you voting in Nevada:
1. A person applying to vote may be challenged:
(a) Orally by any registered voter of the precinct upon the ground that he or she is not the person entitled to vote as claimed or has voted before at the same election. A registered voter who initiates a challenge pursuant to this paragraph must submit an affirmation that is signed under penalty of perjury and in the form prescribed by the Secretary of State stating that the challenge is based on the personal knowledge of the registered voter.