One of the great challenges of wine appreciation is describing what we taste, not just to other people but even to ourselves. Translating what we smell or taste into words is far more difficult than translating what we see into words. While dogs for example experience the world mainly through their sense of smell, we humans are far more visual and we describe the world in terms of what we see with our eyes. From an early age we are encouraged to 'show and tell' but we are never taught to 'smell and tell'. All languages have a rich and sophisticated vocabulary for describing what we see, and we can be very precise in terms of color, shape, size and visual distance when communicating with others - but such a vocabulary does not exist for smells and tastes. There is no semantic tradition in any culture or in any language to describe the things we smell, in the way that we are able to identify things that we see.
In fact the whole process of smelling is limited to a single word: smell. There is a smell coming from the mushrooms; I smell the mushrooms; the mushrooms smell. The same single word is used to describe the odor, the detection of the odor and the action of the odor. Compare that to all the words we have for seeing, looking, watching, gazing, observing etc. We must therefore look around in our personal memories for similar smells and tastes to compare with the wine and then, when trying to share our experience, make subjective comparisons: "it tastes like dark chocolate with a hint of mushrooms and damp leaves."
Another problem is that the part of the brain which processes smells also handles emotions and memory; it's not only the most primitive part of the brain, it's also the most subjective and personal. Smells are chemicals, and as the wine is exposed to air and evaporates, chemical molecules rise from the glass, through our nose to the receptors in our olfactory cortex.
The olfactory cortex which evolved over the eons into the amygdala, is the very oldest part of our brain, and is where emotions and memories are processed. The very earliest job of the brain was to process smell: does it smell good or bad? Is it something I can eat, something I would like to have sex with or something I should run away from before it eats me? Memories of smells were therefore critical to survival and, even in the amygdala of the modern brain, the chemical processing of smells and emotions, memory and desire, are all intimately entwined at a primitive level.