Sourdough starter day 4

Yep, I'm now fairly sure that we have life. Not only are the bubbles sticking around but it's starting to smell a bit like yoghurt and has a sort of stringiness about it when you lift the spoon out; it doesn't just flow but has a certain viscosity to it. We have a sourdough starter! But I'm going to continue to follow the instructions I've got. No point messing it up at this early stage.