It can be the beginning of "starting to think to know what the other person thinks". When people know each other for a long time, they often think they know what the other person thinks or knows. This leads to the idea that if they can complete the sentence of another person in certain cases, they will be able to do so in all cases. This is however not necessarily true.
I believe it is the pituitary gland
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1.) Helps keep you in shape
2.) less likely to get genetic diseases
3.) helps fight depression, anxiety, and stress
4.) can have immediate and long term health benefits