Squirrels have the ability to eat toxic mushrooms as described below. Are there any mushrooms that they can't eat without dying?
According to Dr. John Rippon, an IMA member and world expert on fungal diseases, squirrels have an interesting adaptation that allows them to eat mushrooms containing deadly amanita-toxins without being affected. There are three important chemicals in the amanitas. Two will knock you right off, but are destroyed in cooking. The third one is the interesting one: it consists of the second amanitin, bound tightly to a glycoprotein molecule. When we digest the mushroom, the enzymes in our gut break the bond between the toxin and the glycoprotein, leaving the toxin free to enter our bloodstream, while the glycoprotein is excreted (a glycoprotein is a [protein containing sugar molecules and accounts for the viscous properties of mucus], in case you don't know). What the squirrels have done is line their gut with a toxin-compatible glycoprotein, so that as soon as it gets split from its original glycoprotein molecule, it gets rebound to the squirrel glycoprotein, and excreted along with it. Obviously, the squirrels don't cook their food to destroy the first two molecules, but presumably those get bound in exactly the same way. Thus, squirrels and a few other animals (guinea pigs also, I believe) can eat mushrooms that are highly toxic to other animals with no ill effects. Source