What are those dark seeds in oat flakes?

Anyone who occasionally makes muesli or porridge, must know them. Dark seeds of size about 3 mm, with round's depression on one side, of tough skin and the inside having bright color. Because passed together with oats along the flake machine, they are flattened. In some packages of oatmeal is a lot of them, in some are almost none. But what are they? Are they not harmful to health? Which weeds, apparently growing in fields with corn, do they come from? When I know, I'll write it here. :-)
19.11.2012



I am writing to all parties and yet nobody knows. Seeds of cockle are serrated and irregular, black mustard seeds have a distinctive taste and they differ in shape (round hole missing). A friend came up with a good idea: get raw oats, select these dark seeds and grow the plants, which then will be easier to determine. I'm going for it!
21.11.2012

My friend Ivana Binková wrote that it will either Ivy-leaved Speedwell or Cleavers. Really, it seems to be the Cleavers! The plant is all harmless, even its roasted seeds can be used as a coffee substitute.

Experts confirmed: it is Cleavers