You're walking through a hardware store one day when, all of a sudden, you catch a whiff.
Something you haven't smelled in years.
Somehow, the scent of glue immediately takes you back to your kindergarten classroom, and you spend the next couple of minutes wondering what happened to that kid who used to eat all that paste.
You just experienced what's known as "odor-evoked autobiographical memory".
To put it simply, a smell made you remember something from your past, and it happened because of the way smells and memories are hard-wired into your brain.
There are lots of different cues, like sights or sounds, or even someone describing something or telling a story unrelated to your story, they can trigger memories.
Memories links to smells are often stronger and more vivid.
And studies have shown that they also tend to be memories of your early life, often before you were 10 years old, which is weird, because adults usually experience what's known as a "reminiscence bump", when they don't remember much from before their adolescence.
But smells are really good at bringing those memories back.
These memories tend to be more perceptual rather than conceptual, so you remember a particular sensation rather than a bunch of facts about something that happened.