I have worked with many many chefs who have their thumb over the the top of bottles of oil,brandy,vinegar,wine etc etc. I have never understood it. If you want to control how much you are pouring, just pour a little slower. Is there a need for this? I think a lot of TV chefs are to blame for this. Personally I think it's rather unhygienic, you can contaminate the contents and also you end up with a dirty thumb. Do you do this? And why.