The answer for this is legumes.
The brain region identified lighting up during an fMRI scan in a patient with obsessive-compulsive disorder is the anterior cingulate cortex. The anterior cingulate cortex is part of the limbic system and is responsible for the emotion formation, memory, processing, compulsions and obsessions, and others.
Volumes.
If you put equivalent volumes in a bag, where both weigh the same, the density might get equal.
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It means, process of eliminating waste matter..
