"He owns animals."
Translation:Il possède des animaux.
Why does the accent change from acute accent on the infinitive form 'posséder' but change to a grave accent on the singular agreements? je possède tu possèdes il possède
Is there also a change in the way the sound is pronounced?
Yes, exactly. It's because of the pronunciation. 1st group verbs with an acute accent in the penultimate syllable changes the accent to a grave one when the last E is not pronounced. (Verbs of this for -é+consonant+er become -è+consonant+e(s)). It's because you can't have an acute accent in a close syllable (one which ends with a consonant), thus you can't pronounce posséde. It would be weird and difficult for French people to say it.