3 Answers

Something done without the need to think it over first, it is inborn to that specific species.  Ex. spider knows how to construct a web.  A young turkey poult, hides with the sight of a large shadow in the sky, without mom telling him to.  A sheep instinctively runs away from a dog, wolf, etc. thinking it as a threat.  Baby mammals know to seek the udders of their mother, minutes after they are born.  These are all instincts, they are in their DNA, not taught...

When someone says he has a gut feeling, it is an "instinct"...somehow, and you don't know WHY, you just KNOW.

Just knowing not to go through that door, to answer the phone, to open the box, just knowing w/o basics............