If you could show one item/object to a caveman in this modern world, what would it be?

I was watching Night at the Museum the other day with my kids & my daughter asked me this very question, she’s inquisitive like that.
For those familiar with the movie, there’s a scene where Stiller gives the cavemen a lighter. Naturally they’re fascinated with the notion of fire, particularly from such an unusual (to them) source. So, with that in mind, what modern day item/object would you reveal that would grab “caveboy’s” attention? Keep it clean….ish & you may of course be as humorous as you wish