Despite all the terminology compiled and studied before a proceeding, the way a witness responds to a question can hold the most surprises for the legal interpreter. So we have to change our listening and processing mode for each different style of responsiveness. We base our performance on canons of professional responsibility for completeness, not paraphrasing and not omitting what is said. But if we don’t catch every word spoken, we run the risk of failing our oath.
Witnesses respond according to their reaction to the question and to the way the subject matter is emphasized. Sometimes they are intimidated by the process. Sometimes they show anger while facing the representative of those they hold responsible for damages or those who sued them. It is an entirely personal behavior no matter how much preparation they were given by their lawyer.
The easiest back and forth to interpret is the orderly question followed by the short response with no heightened emotion by either party. The other extreme is the witness who either launches into or builds up to a rapid free flow of extensive narrative, without a pause whatsoever. I call this the Waterfall Witness. 
The interpreter needs to develop three skills to master the rendering of waterfall testimony.
1. Prediction. Observe the witness long enough to catch any emotion beyond complacence. Note the length of the responses to the personal history questions. If they are beyond the scope of the question, you have warning of a pattern there. If the witness dissects the question in the answer, that can erupt in long winded hostility. Grief lends itself to listing memories. Anger becomes confrontation and repetitive phrasing of the stated issues.
2. Pace duplication. As linguists we are listening in order to render. You will have to erase any reaction to the content of the testimony in order to retain it. The best way is to keep pace with the speaker. Duplicate the tempo of the speaker with either your notetaking or your simultaneous interpreting.
3. Keep track of the topic. The waterfall witness will add topics and stray off topic. Your notetaking should highlight the new topic and the key word they use. I have even drawn a hierarchical map with arrows charting the response from topic to topic.
I have found that in a deposition the attorneys rarely interrupt a waterfall witness simply because they want to hear everything this witness may possibly have to say about the issue. If they do it is through an objection. But in trials, attorneys will interrupt via objections and the Judge will interrupt with an instruction. So the interpreter also has to monitor the point when the judge interrupted during the witness’s testimony for the court reporter to hear that clearly. Then the full instruction to the witness has to be interpreted along with their response. Even then, you cannot rest because the objecting attorney may reply with a “Thank you, your honor”.
The interpreting mode can be an issue. Trying to take fully accurate notes of a 300 word missive at the pace of emotional discourse is risky. I expand my note taking to include topic with key words and identify the order in the response. I go through a lot of paper. It is easier to go into simultaneous mode which can be done in a deposition. But in court it is hard for the jury, the court reporter and the judge to hear you not to mention the attorney further back in the courtroom. If you are allowed to use simultaneous, I suggest getting permission from the Judge to step forward closer to the court reporter and then speaking louder.
All told, taking on a waterfall witness is not for the novice interpreter. So practice a lot and go watch one in court. Remember, witnesses have the right to testify in the form that is natural to them. So, it is up to us to raise our skill level to meet this challenge.