All of have probably forgotten to do this at one time or another--look at the right hand side of the census page for the 1840 enumeration. Sometimes it can contain a big clue.
This is part of the 1840 census enumeration for Elam Blain, Junior, in Harlem Township, Delaware County, Ohio, in 1840. And yes, it's spelled Elam Blain on the left hand side of the page and Alam on the right hand side.
I've been analyzing Alam's Revolutionary War pension file for an upcoming series in Casefile Clues. I won't repeat all that analysis here, but thought the 1840 census listing of Revolutionary War pensioners might be a good reminder.