Occasionally certain verbs are very important to the topic, and when you think about it, you may determine that readers will think of these verbs and try to find your paragraph by trying to find them in the index.  In these cases, do not hesitate to make index entries out of them if they will help your readers more easily find material they are looking for.  While this is not traditional, in this author's opinion, the purpose of the index is senior to that tradition.