The party is up to the ol’ heist shenanigans again, attempting to break into the home of a local merchant. They peer through a window and spot a dog that looks maybe guard-doggish, but maybe just a nice dog. “I cast Mage Hand,” says Honey-bells. “Then, very gently, I use the magic hand to pet the dog. I want to get a sense of its disposition before we go inside. Should I make an animal handling check?”
Should he?
Mage Hand reads:
A spectral, floating hand appears at a point you choose within range. The hand lasts for the duration or until you dismiss it as an action. The hand vanishes if it is ever more than 30 feet away from you or if you cast this spell again.
You can use your action to control the hand. You can use the hand to manipulate an object, open an unlocked door or container, stow or retrieve an item from an open container, or pour the contents out of a vial. You can move the hand up to 30 feet each time you use it.
The hand can’t attack, activate magic items, or carry more than 10 pounds.
Rule as written, it would appear that Mage Hand cannot be used to pet a dog. The problem here is that petting a dog is not among the listed things you can do with the spell. Mage Hand is somewhat odd in its text in that it provides a list of things that appear to be examples, but without the appropriate “such as” or “etc” language. That leaves us with the basic principle of do what the rules say, don’t do what they don’t say. As written, Mage Hand can only be used for the listed purposes.
To get more technical, we’d use the canon of statutory construction expressio unius est exclusio alterius (“the expression of one is the exclusion of others”). When a rule lists things out, and does not expressly make them representative examples of a larger group, it should be interpreted as being limited just to those listed items.
But what if we engage in a little judicial activism and tweak the language:
You can use the hand to manipulate an object, such as opening an unlocked door or container, stowing or retrieving an item from an open container, or pouring the contents out of a vial.
That doesn’t help. Doors, containers, and vials are all objects. Everything in our list of examples is manipulating an object, and a dog is not an object, it is a creature.
It may be disappointing that you cannot use Mage Hand to pet a strange dog without risk of getting bit, but maybe that allows us to use it as a way of detecting something far more dangerous than a guard dog: mimics.
The party sneaks inside — it turns out the dog is equal parts sweet and lazy and doesn’t make a peep. They go into the cellar and locate a lockbox, likely where the merchant keeps his money. But also possibly a mimic. “I cast Mage Hand,” Honey-bells says, “and use it to pet the lockbox.”
“You pet the lockbox,” the DM says.
Honey-bells’s player get a bit suspicious, “Is a mimic that has polymorphed into an object considered an object or a creature for purposes of Mage Hand?”
“Oh, hmmm… not sure,” the DM answers. “But, you still do pet it.”
The player isn’t buying it. “I use the spectral hand to smack the box.”
“Mage Hand cannot attack.”
“Ah! So that means it’s a mimic! It wouldn’t be an attack if it were just an object.”
The DM clears his throat, “Chapter 15 of the Basic Rules refers to attacking objects, so I’m ruling that smacking the box would be an attack and so the hand cannot do that.”
“…I use the hand to lift the lockbox up to the ceiling and then drop it.”
“The lockbox weighs more than ten pounds.”
“Fine, forget it!” the player finally exclaims in frustration. “Honey-bells picks up the lockbox.”
“You find your hands stuck to the box. Roll for initiative.”