This is a very good question! and it would happen from time to time! In an experiment, when an individual (could be human or non-human animal) gets angry or frustrated, we will encourage the individual to continue to participate in the task. However, if they have chosen to give up, we do not force them – we respect their decision. This is the same for non-human animals – we allow them to go home or give them a few minute more to calm down and if they do, we bring them home.