Lyrics question

When I first heard Grazing in the Grass (on a crackly AM station) I couldn't make out what this refrain was. When I finally figured out the lyrics, I wondered how in the world they managed to sing what I found to be such a tongue-twister.

From the ridiculous to the sublime: from my observation this morning some hymns have lines that are a bit harder to sing--the syllable sounds don't make for easy transitions from one sound to another. If you have a syllable ending in "d", you need a little extra air between that and the next one that starts with a "t". I suppose syllables that blend together smoothly can be called "slurs" or something similar, but I'm not familiar enough with musical terminology to say.

Is there a term for the juxtapositions that make it harder to sing smoothly? Jackhammer words, maybe?

I suppose if the music is stacatto, these might fit better than those that allow "slurs", but most of the time, or for spoken poetry, I'd think them worse.

At any rate, I wonder what terms I should use in searching to learn more.