When milk level is more than 0 pairs of boobs () start appearing on exciting members profile pages.
You can find them and collect "milk" by clicking on them. This will give you points.
It's random, you are not guaranteed to find them. They only appear on profile pages of the members who have excitement rating of 600 or more. Your chance to find boobs is about 1/6 per page but probability to find milk in them drops drastically with each pair of boobs found and also the more points you already have the less is probability to find points in the boobs.
Those boobs are always hovering somewhere over the thumbnails on the member profile (1st page only). You should carefully look through the thumbnails of images (do not go to full size images) to find the boobs.
There are several limitations:
1. You should turn off invisible mode if you have it on, otherwise this won't work.
2. You should give at least +1 during past 8 hours to the excitement rating of any member you like.
3. You won't find boobs on the profiles that you already visited during past 1 hour. So do not try to refresh same profile - this won't work.