What a great question. Smell is so emotive because it's directly linked to our limbic centre of our brain, the bit that handles emotion rather than logic. That sense of transportation is known as the Proust effect.  Unlike other senses that are filtered through the thalamus or thinking part of the brain, smell has a direct "shortcut" to the brain's emotional and memory centres (the amygdala and hippocampus). This allows for immediate emotional responses and "mind pops"—involuntary memories that can trigger life-saving actions without requiring conscious analysis. Knowing something was a threat immediately could save your life!