This an excerpt from an arragment to the song "Hakuna Matata" from the movie "The Lion King":
Why are there percussion notes in the vocals?
What you are seeing is the standard notation for something that is spoken, or chanted. The syllables are intoned at a specific rhythm but not at a specific pitch.
The technical term is the German "Sprechgesang" and related, "Sprechstimme". Literally "spoken singing" or "spoken voice". Like other answers have stated, the "notes" in question indicate that the words should be spoken in the notated rhythm according to the stems, but the exact pitch is immaterial.
This technique of writing can be fudged a bit, as the cross-head notes (the standard notation for Sprechstimme) can be placed on different lines to indicate a general rise or fall in the spoken "pitch".
That is because it's spoken and not sung.
This song in the movie:(skip to 1:14)