The side wall bubble is when you put a very small bubble onto the side of a modelling balloon.
It is easier to do with a slightly softer section of balloon and with the balloon folded.
The bubble would be twisted into the side of the balloon where the fold of the balloon is made and acts as an attachment point.

That's easy for you to say; or draw. Sometimes I can do it straight away, and sometimes it takes ages. And sometimes I give up. Any additional tips to make it foolproof?