When Indy and Marcus meet with the government men on the stage of the auditorium, Indy puts a very large book on the table. At that point, or soon thereafter, one of the two large clasps holding it closed is open. When Indy opens the book to show the picture of the ark, he has to unhook both clasps.

I know it's nit-picking, but I've watched the movie dozens of times and it bugs me.