How can you take 9 toothpicks and make ten without breaking the toothpicks?
TEN (every line making the letters in the word ten is one toothpick. There are nine lines you draw when writing ten, so there are 9 toothpicks making TEN).
Jack tells Jill, "This isn't the $5 bill you left on the the table. I found it between pages 15 and 16 of Harry Potter."
Jill retorts, "You're lying and I can prove it." How did Jill know?