What is Dead

We were in LA recently and went to see the Mummies exhibition at the California Science Center. We didn't think much until we bought the tickets and were in the line - Ashir asked -

"But Papa - what are mummies?"
"Mummies are...." I paused, I was going to say dead but he didn't know dead yet
"Mummies are bodies of people or animals from very old times"
"Why?" (Standard follow on question for everything)
"We will see once we get in"

The first exhibit, presumably to awe people, was that of an Egyptian boy, very well preserved for a mummy but grotesque for a 3 year old to watch. It had its teeth intact, shirvelled leathery skin and some hair..
"What is this?"
"Hmmm this is a mummy of a boy.....when people died in old times they made mummies of their bodies" I had thought of something by then.
"What is dead?"
"Dead means that people can't move any more. Like when you squished the bug the other day.. it died. Same thing happens to people"

Surprisingly, he didn't ask any more questions on dead, kept looking at exhibits, asked other questions but not about dead.
Several days later back at home while playing with his trains he was speaking out a story aloud. This is how he plays alone, just making up new stories and speaking out loud. I was working on the computer and between thoughts looked up at him narrating the story -
"Gordon was going so fast that he could not apply brakes in time, round the bend he slipped and bumped hard into Thomas who was taking a washdown by Tidmouth sheds... he hit him so hard that he fell down and did not move.. he was dead"