I have come across this situation many times. For example:
Interactive e-books can not only show characters' movements and facial expressions but also can let the children (readers) choose what would they do under the scenarios.
Should I use plural for those words? I feel it may not be necessary but characters have many movements and facial expressions in an e-book and there are many scenarios in an e-book too.
I tried searching Google for it but I cannot find explanations for this kind of situation.