A **simile ** is a comparison taking the form “As a is to b, so **c ** is to d”. It highlights the way in which one relationship between two terms corresponds to another such relationship. Example: "As ‘Shakespeare’ is to ‘Hamlet’, so ‘Emily Bronte’ is to ‘Wuthering Heights’ ". The relationship is ‘the first term is the author of the second term’. Second example: "As ‘nose’ is to ‘dog’, so ‘trunk’ is to ‘elephant’ ".
A **metaphor ** is a transfer or substitution of context intended either to assist explanation, or to achieve a given dramatic effect. When Meatloaf sings that he’ll be gone “like a bat out of hell”, that’s a metaphor. He isn’t actually intending to transform into a bat. He is using the very dramatic metaphor of a bat flying quickly and elusively from a place it doesn’t want to be to illustrate how he will feel and behave in the morning. Metaphors can be short and sweet, or extended and complex. As an example of an extended metaphor, one could cite entire movies or TV series (like ‘The Invaders’ from the 60s) in which the threat of invasion by beings from outer space served as a metaphorical expression for the fear of invasion by communists.
Ouryl, no disrespect, but either you have misunderstood what your teacher said or you need a new teacher.
To answer the OP.
" “That man has a nose like a bloodhound.” - Simile. "
It isn’t a simile. It’s just a comparison, or it could be regarded as a very simple metaphor. It would only be important to point out that the speaker is speaking metaphorically if there were any danger of his comment being interpreted literally, i.e. that the man’s nose is really shaped like that of a bloodhound.
" “Bob’s a real bloodhound - his nose is very sensitive.” - Metaphor. "
Same again. It’s just a comparison, or possibly one could call it a very simple metaphor.
" “If Bob were a dog, he’d be a bloodhound.” - ? "
MLS is correct, in that this sentence does use the subjunctive tense. Just for completeness and for anyone wondering, the ‘subjunctive’ tense is used when denoting theoretical or conditional possibility, as opposed to the description of an actual fact. It is usually signalled by the conditional ‘If’ at the start of the phrase. The shift from “He was” to “He were” is one indication of the use of the subjunctive tense. “Bob was a pianist.” is a declarative sentence in the past tense. It tells us about something factual. “If Bob were a pianist, I imagine he’d be a fairly good one.” tells us about something imaginary or hypothetical, and so the subjunctive tense is used.
" “If Bob were a dog, he’d be a bloodhound.” - ? "
This is not a simile, although it could be recast as one. It is not a metaphor, or at least not a very good or well-expressed one, although it could be recast as one. It is just a statement about Bob, comparing him to a bloodhound.