I was reading a Wallace and Gromit story to my (now 5-year-old) son, and he energetically pointed out
|son||Look, a grandfather clock!|
|me||Yes, that's a grandfather clock. It's about to fall on top of Wallace!|
|Wallace||That's just the thing, my lad, we'll have to turn back the clock ...|
|son||What's "turn back the clock" ?|
|me||Well, suppose something happened yesterday that you weren't happy about, so you decide to <blah blah long-winded explanation of expression with digression into the role of metaphor in language>|
|son||Oh, you mean he builds a time machine?|
Duh. I should have realised time travel is a standard part of every 5-year-old's vocabulary.