I can follow that most of the text is in the (futur d'anticipation).
However, I am wondering why the text switched to using the infinitive (entendre), in the last sentence? and why not use the Gerondif -en entendant. like at the beginning of the fourth sentence.
Mo,
the links below discuss the use of the French infinitive, including in the situation in the sentence you refer to - a verb used as a noun as subject ( or object ) of another verb.
It is a situation in which in English we could use the present participle, but that is not the case in French.
Have also included links to discussion of the present participle and gérondif, neither of which is appropriate to use in this sentence.
Another important difference in the 4th sentence of the text is that simultaneous action is being described.
https://french.kwiziq.com/revision/glossary/verbal/infinitif-infinitive
https://www.thoughtco.com/french-infinitive-linfinitif-1368866
https://french.kwiziq.com/revision/glossary/verbal/infinitif-infinitive
https://www.thoughtco.com/french-present-participle-1368923
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