How in Christ's name do they do that?

So people ask me on a semi-regular basis how to make things. They've seen something on the internet and want to have a go themselves and haven't been able to work out themselves and so try so other silly sod for the answers and sometimes, that's me. I can help with some stuff, I have enough knowledge of the basics to do most simple things in resin, but bubbles, bubbles escape me....
I saw these beautiful Sobral pieces early on in my resin adventures and loooooved them. Hey, what's not to like, they're playful and pretty and colourful and awesome. I also just loved the bubble pattern, I have a bit of a thing for dots and nubbles and other ball like adornments on some days. I was able to work out how he made his lurvely stripey pieces (see top) by either layering colours in your mould, or casting a chunk of layered resin in a big tray and then cutting out your bangle (to get vertical stripes rather than horizontal you'd need to put your chunk, or your mould on the side), but no bubbles. Couldn't find tutes on how to.... nothing
Then I came across this picture on the Sobral website where it looks like a squeezy bottle of liquid resin is being squirted into... clear resin? Water? Boiling water? Not sure kids and herein lies the problem. I actually had a stab at this with resin and water and no luck for me. I got a mess and that's about it.
Not sure if the technique perhaps lies in the fact that many resin companies use acrylic and have to heat set it somehow to cure it or what, pretty sure they aint using stinky polyester resin.
But, dear non-readers and random people who stumble here, if you reckon you've got it sussed, let me know in the comments below!