Idiom ~ "follow your nose"

I'm helping another resident of the Crown Center understand idioms in our English language, and his latest question was about the meaning of the phrase "follow your nose."  What a strange thing to say!  What does it mean to "follow your nose"?

1.  trust your instincts.

"You are on the right track, so follow your nose."

2.  move along guided by one's sense of smell, following a scent in an attempt to find its source.

"I thought I smelled something baking, so I followed my nose to the kitchen and found my mother icing a cake."

3.  walk straight ahead (thus walking in the direction that your nose is facing).

"Should I turn here?"
"No, follow your nose and keep walking straight ahead."

I combined several online explanations and used the definitions that come closest to my understanding of the phrase.