My husband has 8 young nieces and nephews. Several years ago, I came up with the idea of getting them some unopened geodes (hollow rocks) that they could open up and see what crystals were inside them. We filled and wrapped a box for each child.
When it was time for the Christmas party, they were all excited about opening their gifts. Beforehand, they kept asking what was in those heavy boxes, and my husband kept telling them it was a "box of rocks" because they'd all been naughty that year. Naturally, they thought he was joking.
You should've seen their faces when they opened their gifts, and sure enough, they'd each gotten a box of rocks!
They didn't know WHAT to think! It was all we could do to keep a straight face.
Hubby teased them for awhile, then finally explained what the rocks really were. They absolutely LOVED cracking open the geodes, and they still talk about their "box of rocks" to this very day. It turned out to be one of their, and our, most memorable Christmases.
