[And THAT just makes Walter laugh, though he cuts it short so as to not give the wrong impression.]

It's the events that surround a memory, that combine with the content; whether everything looks taller or shorter than they do for you right now, whether the sky looks like a color you can see from Earth - whether there is a sky.

Names and emotions can be tied up in context, too. People you've never met, in places you haven't been to, or don't look like places you've ever even seen.