what food can kill dogs instantly . However, certain foods can cause severe and potentially fatal reactions if consumed in large quantities or if the dog is particularly sensitive to them. For example, ingesting a large amount of xylitol, a sweetener found in some sugar- free products, can lead to a rapid drop in blood sugar and liver failure. Similarly, consuming excessive amounts of certain toxic foods like grapes, raisins, or chocolate can lead to serious health complications that may be fatal if not treated promptly.