Yeah, it was already neatly explained.  Very good job!

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    In addition to it, and stretching the class a bit, you can make your pupils see what happens with the some words, when used as subject of the sentence or or as a verb (ING).

    LIFE    (subject)

    Anger never dies, It's part of life...

    A ira/raiva/cólera nunca morre, (ela) é parte da vida...    

    LIVE    (livING)

    Anger never dies, It's part of living...

    A ira/raiva/cólera nunca morre, é parte do viver...

     So with time, they will do what you did.   Will notice that if the verb act as a subject

of the phrase, it will have the ING particle joined to it (to the verb, I mean).