From Mouth to Ear to Brain to Notes to Paper--For Starters

When using census records--both searching and interpreting--think about that word got to your screen.

Your ancestor said it.
The census enumerator heard it.
The enumerator thought about it.
The enumerator wrote it down in his notes.
The enumerator put it in his actual census report.
It was microfilmed.
It was digitized.

And maybe somewhere in there is was transcribed or indexed, in which case it was read.

At any (or every) point in the process there could have been a misunderstanding. Multiple misunderstandings compound errors and result in entries that are a far cry from what was said by your ancestor.