If left alone, a dog would eat the banana. This may cause them to experience some stomach discomfort.
Based on current knowledge, limited information is available on dogs eating bananas; more data is required to determine if it has negative impacts on dogs. Dog owners reported that their pets ate bananas without displaying any symptoms of diarrhea or vitamin deficiency at lower than human-estimated dosage levels of 50 mg/kg BW/day for small breeds and 30 mg/kg BW/day for medium breeds (Porter R., 2013). Reasons why these dogs were not affected include difference in intestinal flora composition, different nutrient requirements between species, and minor discrepancy between animal studies and human studies.