Preheat the oven to 375 degrees.
Mix the flour and baking soda in a bowl.
Combine peanut butter and milk in another bowl and mix.
Add the wet mixture to dry mixture, and mix them well together.
Put the dough on a lightly floured surface and knead thoroughly.
Roll out so dough is 1/4-inch in thickness, then cut out shapes or use a dog bone cookie cutter.
Lightly grease a baking sheet and put the cookies on it. Bake 20 minutes. Check on them frequently as they can burn easily.
Cool on a rack.