How did it help him ‘hear’ the note?
I can only suggest you play it and see … it should sound familiar.
It was to him … it was the first tune he ever learned to play and he knows these note intervals like the back of his hand.
Just in case you didn’t figure it out – the lick - It’s this of course!
Now don’t go pretending you’ve never played that riff before!
Thank you @Richard_close2u for that. That should be really helpful. I’m not at this point yet, but I’m itching to try it out later. 
Pretty cool Richard, just gave it a chop. Fun & a great way of training the ear! I’ve been plugging my guitar into a DAW and running note detection to check if my bends are in tune in bend practice, which is really dull vs something like this.
1st riff my friend taught me when I was 14. I think it may be the 1st for a lot of people
I’ve just given that a try Richard. Very cool and what a great practice piece to make sure your note is sounding right.
A first time for me and it happened here. 
@jkahn I too like to ‘supplement’ my ear with an aid. I use a pitch monitor app on my phone/tablet. That may be more convenient than the DAW.
@SgtColon But you did know the song and riff, Stefan? I have to ask as I know many folk here are more into the 90s and beyond and have limited exposure to the music of the 70s.
We were chatting about classic Stones albums in another Topic. Given the riff has been mentioned, if you have limited exposure to Deep Purple, I suggest you put Made in Japan on your Spotify list 
GOAT debates rank up there in the most futile of all activities IMHO but if one started that debate on live albums, I feel safe in saying Made In Japan would be among the albums discussed in the debate.
Oh yes, I know the song, even when I played it I could still tell what it was.
Added. 
I think there is some much back catalogue stuff I need to investigate. So much cool music 60’s-70’s. I’ll never need to listen to a modern track again. 
And of course you can always listen to Deep Purple’s latest release, Turning to Crime (2021) … would that count as ‘modern’ 
I can’t recommend it personally as I have listened to it. And the band line-up is different to the Made In Japan lineup (Lord retired and passed away, and Blackmore was in and out a few times, before finally replaced by Steve Morse)
Apologies Richard, have digressed from the fine riff trick to learn a tone interval.
Oh was that Deep Purple ? Smoke on the what ? Never heard of it, honest guv.
There’s a good reason why, it’s one of the forbidden riffs in the guitar shops 
Is that supposed to be Smoke on the Water? Never heard it played like that. Mind you it’s may be over 30 years since I last heard it!
It is not the riff how it is actually played in the proper sense.
The above is in a different key and only uses single notes whereas the riff uses double-stops.
But the intervals are the same - the ‘sound’ is the same.
No, a slide, like a bend or hammer-on etc. does not need (should not need) a separate pluck to ring out.
OK, but you could pluck if you wanted to. Just like you could pluck at the top of a bend. Didn’t the Beetles do that?
Does Justin have a lesson or part of a lesson about this?
Sorry Stuart, I had meant to reply before now.
You can pick if you want. The skill of sliding is not the focus of this exercise. The focus is to train your ears to hear the intervals and notes in a recognisable riff and then to bend accordingly.
I like this very much. The slide as a reference sounds much more similar to the bend, compared with playing two separate notes, because you get to hear a continuous shift in pitch from the lower note to the upper.
At least to my ear, it’s easier to judge whether my bend ‘sounds right’ against the slide.
Great tip Richard, thank you.
Thanks Brendan.
