It has to be a 'glass cutter'.
methinks a boiled egg! He'll definitely know what's in the box after a few weeks.
I'm too literal for this, but will laugh with the best when it's guessed, in a few weeks.
Cro, you are too funny!
Oh! I see Cro suggested a glass-cutter, too (Happy Christmas, Cro)!
Thank you Claire... and a Happy New Year to you.
Cro and Claire, the both of you are more clever than me!