Im pretty sure it is in fact bits and bobs of herbs Carlos. I experienced the exact same problem with my screens sitting crooked and wonky in the bowl, no matter what I tried to keep it flat and snug to keep particles from falling into the bubbler. I also expressed my preference for the XL bowl design where the dimples are lower so that the screen sits firmly and snug without any gaps at the edges. And @Carlos8400 I can certainly understand how you found that to be a nuisance in the deeper bowl Sebastien sent you. The XL bowl is not too deep that it makes it too tricky, but I can tell that if it was just a little deeper, or narrower, it could be very tricky getting the screen in and out of that more tightly fixed posistion. @Echo , what you want is some of the "Arizer basket screens". They fit upside down into the underneath of the bowl and keep all the herb particles out of your bubbler.