I have come across expressions like:
I can smell a rat.
It smells fishy
They could smell his fear.
I understand what these mean. However, I would like to know if there is a common meaning behind the use of the word/verb smell.
For example, could you say that smell represents a a feeling of being aware in each? Also, why do you think that smell is used?
Yes, a 'feeling of being aware' is a good way to put it.
I think it's used because we often become aware of the thing to which a particular smell is associated before we become conscious of the smell itself. Instead of thinking "that's salt water" we think "we're getting near the ocean", or "there's a bakery nearby" instead of "I smell hot bread". We aren't used to putting smells at the fore of our consciousness, but it still works "in the background", so to speak, and so we have expressions indicating that we think we perceive something without visual or audio evidence of it.
EDIT: I just realized, also, that I often don't know exactly what the smell is, only its association. I can't tell you if the smell is hot bread, or hot yeast, or some other product of a bakery, I can just tell you that I associate that smell with an operating bakery.
Part of the problem is that your three examples are not necessarily all being used in the same sense. The first two are definitely being used figuratively to mean "I sense that something is improper but cannot prove it."
The third may be being used literally to mean "I can smell the pheromones typically released when in fear," or it may be being used in the figurative sense.
