It's clear that tatoos can be enchanted, so the mark or maybe a tatoo in the animal hide could be enchanted to make them for example a half-human or make animals commmon breath fire?
What do you think?
It might take some custom modifications to a lab to enchant an animal (or human)*, to make them into an enchanted item, but in theory it should work fine. Warping would be unavoidable, I'd think.
(* The distinction between enchanting a part of their skin (a scar), or some ink in their skin, and the animal itself is a fine one. I would think the two would become "the same", otherwise it's the ink that can breath fire, not the animal - and I don't see that working out very well.)
The big problem is "Activation". It might be a bit tough, since many (most? all?) animals would be hard to train to make a specific, unique gesture only when they want to "breathe fire", or even (with a mental link) to "think" of something that they normally, instinctually cannot do - Animal "Cunning" does not, as described, allow an animal to make selective use of a tool, even a magical one, such as you're describing.
As an example, if you, somehow, gave a dog a shotgun, mounted it on his collar, and taught him how to fire it (maybe by scratching his ear just right) - do you really think they'd only fire it at burglars? Would you really want it walking around anywhere near where you or yours walk around?
Rego Animal Lab Total for Hermetic Animal Training explained in RoP: Magic should work to tiggers.
The Tatoos in tatoo magic explains that the Effect would be designed in any case for that user, or that result like if the user is the caster.
After of that too it is the option for a Enviromental trigger, and a continuos effect. Warping? Sure. But with that you can have a very special Covenfolk. And a nearly accesible to make the Boon of Magical Covenfolk or Magic Warriors to the a Covenant.
The Idea comes from HoHMC:
I'm guessing that there is nowhere in the rules that specifically, clearly states that "the user" has to have "Intelligence" rather than mere "Cunning" - that is, that they have to have human intellect rather than animal instincts and understanding.
But I sure as hell believe so. But if you want kittens or rats or earthworms to be able to "intelligently" decide when to trigger and how to target magical devices, knock yerself out.
It's needed action phisics, or simply the simple Sun duration, two uses day and enviromental triggering, simply and effective. Or triggered by other thing, connected by other Trigger efect, some emotion or similar.
Constant Effects? Oh, that'd work fine - an animal that breathes fire with each breath, certainly, I can't see any problem with that! 
(I clearly misunderstood the intent!) 8)
(If by "action physics" you mean "a triggering action" - the obvious problem is that the animal may not wait until the best moment to activate the item - they don't comprehend the cause/effect and the need for restraint, as I suggested above. If an animal is trained to do something fancy, they might then do it at any time by accident - just because you train them to do that fancy move and trigger it at the bell doesn't stop them from triggering it at other times as well.
Triggering by animal-emotions would work, but need an InAn effect to trigger them, and now you're talking Greater Enchanted Device. And I've seen dogs react strongly to mirrors, toy animals, and oddly shaped logs... you have fun with that.)
A constantly firebreathing dog in the tunnel leading to your sanctum certainly would deter most visitors!! Much better than modern xray security devices!
Well since shouldn't be with penetration... the Un-gifted/Hedge wizards would "fun" really.
It would also deter the dog, almost immediately. Dogs tend to sniff certain parts of their own body quite regularly... (ouch) 
sniffing, air in
breathing, air out
What could possibly go wrong?