I once played a mage in a Live Action Role Playing adventure, and cast a spell to summon a water elemental, to fight on the side of the party against the monsters opposing us.

One of the GMs appeared, appropriately clothed, and proceeded to give the fastest lesson ever on being specific. Because, the way he played it, the water elemental would obey commands, but was malicious, and where possible would misinterpret the command, or do things I'd not yet specifically forbidden it to do.

elemental appears, moves to nearest party member and starts hitting her
Me: stop!
elemental stops walking, but carries on attacking with its arms
Me: stop attacking, don't do anything until I tell you to, then do only what I've told you to do
Me: those people over there points are the enemy - go attack them
elemental goes attacks a wall in the indicated area, then returns and stands on top of a party member, not doing anything but immobilising them
etc.