She picks up things!

Miss Jones had been giving her second-grade students a lesson on science. She had explained about magnets and showed how they would pick up nails and other bits of iron.

Now it was question time, and she asked, - "My name begins with the letter 'M' and I pick up things. What am I?" A little boy on the front row proudly said, - "You're a mother!"

Source: http://humour.webwweb.com/