Bragg blows air into a small tube in order to give shape to the glass. He says that the tube is a safety precaution because if he was to blow directly into the glass without the tube, there is a potential that the vapors could ignite and be sent back to his lungs.
![](https://immunemedia.org/wp-content/uploads/2013/12/IM_UO_dyck_glass-07.jpg)