The Last "Help" in "Can't Help Falling in Love"
A standard Presley technique is to prolong a note with a slight vibrato. I would actually call it a shimmer. The easiest way to add vibrato to your voice is to sing in operatic style. Presley does not do this. The first part of the note is normal voice, then the shimmer is added.
This song ends with a repetition of the phrase "For I can't help falling in love with you". On this "help", as on every other help in the song, Presley begins with normal voice and extends the note with a shimmer. About 2/3 of the way through the note, he transforms into an operatic voice. The operatic style is sustained into "fall", but I think is gone by "ing".
Interpretational Effect. The effect is electrifying. This is the best song note that I know of. It would normally be subliminal, but I enjoy it even more now that I am aware of it.
To speculate probably triggers the same response as any of Presley's operatic endings. The song "It's Now or Never" is a classic example -- Presley teases us, then finally does his operatic ending. In "Devil in Disguise", he uses normal voice when singing of her charms then switches to operatic when he starts singing the words "your the devil in disguise".
But Presley doesn't do a full operatic ending, he starts it late, and the duration is so short as to make the effect unnoticed.
Can you do this at home? With practice, I could learn to shift my voice to operatic in the middle of that note. However, for me, the contrast is not enough to have any effect. So it requires at least some vocal athleticism.
Adding a shimmer to your voice will probably make you sound more like Presley. If the shimmer becomes a noticeable vibrato, it is too much.
Other SingersIn the Song "Strangers in the Night". Frank Sinatra produces a similar effect. It is on the long note of the word "you", in the phrase "told me I must have you". He adds a shimmer about half way through the note, presumably to extend the note just as Presley does. Then at the end he very briefly switches to a different voicing. I don't understand it, but if you are listening for it, it is easy to hear because the vowel sound changes a little. I do not know the function of Sinatra's change. It might serve simply to complicate the phrase. Sinatra wants to hold the note all the way to the start of the next phrase, and I suspect that would sound a little trite without any more changes to the note.