Oracle Text

You may tap or untap target artifact, creature, or land.

Card Rulings

10/4/2004 This is not a toggle effect. If you use Twiddle to tap a card and before it takes effect your opponent taps it, Twiddle will not automatically untap the card.
10/4/2004 The decision whether or not to tap or untap is made on resolution. This is not a modal spell.