There's 2 packets of un-eaten packets of muesli..but the mice put holes all the way through it and ate it!! GRRRRR!! So could dogs and cats eat muesli?

No, muesli is of no nutritional value to dogs or cats. It's pure grain. Throw it out!

You might want to consider getting a pest exterminator in to get rid of the rodents in your home.

Sure they could - only if they liked the taste of it of course. In my life, I have owned 7 cats, and they have all developed odd tastes. Tallie, likes to eat Fibre X - a fibrous breakfast cereal made of different seeds and grains. Hamish likes to eat Weet Bix and Angus liked to eat Cornflakes. Your dog and cat may eat the muesli if you add some milk and honey to it, it may actually really appeal to them that way. But this shouldn't be their main food source of course, because cats are carnivors and dogs are omnivors, meaning they need meat for protein to sustain their health and well being :D pets question and answers,www.5d2d.com
Ps. when I saw this question I thought - yay! Someone is as random as me :D hehe

Additional note : Re: Moondog:
Cats are the best, inexpensive pest controllers out there. Your cat will love to hunt and kill these vermin, and soon you should be rid of your pest problem. If however, they have bred somewhere, do call a pest exterminator.

I agree with Moondog.

Your pets might even have allergies to stuff in the muesli, or have a bad reaction to it. If you've seen the film "Shirley Valentine", then there's a vegetarian Bloodhound which eats muesli - as weird as it sounds, this is just a fictional screenplay / film, so don't try it!

It could be full of sugar, honey etc. which are not good for cats or dogs. Throw it away and buy a mouse trap.