Most ballots should be accepted by the scanner without issue. However, there are a few cases when the scanner will ask for additional confirmation before accepting the ballot.
One situation is if the voter inserts a blank ballot. This may happen if the voter accidentally does not mark their ballot or perhaps wishes to cast a blank ballot as a protest vote. In this case, the DS200 will confirm they want to cast a blank ballot or give them the option to return the ballot and allow them to vote.
Another situation is an over-voted ballot. This happens when a voter filled in too many ovals in one or more contests. For example, they were only supposed to select one candidate for Mayor, but they couldn't decide and filled in ovals for two candidates. The DS200 will give them the option to cast the ballot as it is, informing the voter that the over-voted contests will not be counted (other properly-voted contests will be counted). Or the DS200 can return the ballot to the voter, which they can SPOIL and exchange for a new ballot.
In both of these situations, clear visual and audio cues will indicate the scanner did not accept the ballot. If you're not sure how to handle them, remember your favorite word: "Chief!"