If you suspect or know that your dog ate a poisonous plant, you should call your veterinarian immediately. They may recommend bringing your pet in. Depending on what your dog consumed and the symptoms they may administer IV fluids, or give them activated charcoal. This will absorb toxins and expel them from the body. In the case of Monstera plants, you may want to wash out his/her mouth with water or give them a little bit of milk.