Mercury
The moments of deep memory bubble up on their own, like with childhood experiences. Most of the time we're not aware of what preceding thoughts bridge back to the recollection, or why. Remember mercury? We had no good sense as kids back in the late fifties, and lots of free time. Of course, intentionally breaking a thermometer felt wrong to do, so a moment of conscience tried to derail the idea. But the attributes of the element were way too alluring for a boy who imagined it was something magical from wild outer space. A metallic liquid that formed into little droplets, we mindlessly rolled the mercury around in our palms, fascinated by its bizarre nature. We were totally oblivious to any risks of toxic exposure, it was a quick toy, temporary and taboo. Mom never knew why her thermometers vanished, as childhood, too, disappears with no notice, perhaps only a bit more circumspect caution, and a bit more common sense.