Sentience is the relevant criteria because it matters morally if a being can be harmed and caused pain. If we examine the reason why it is wrong to torture a dog it is not any of the many characteristics of a dog we can list such as the species they belong to or that they have a certain type of body shape. If it is refined down to the most fundamental level of why it is wrong it is because dogs are sentient – torturing them causes them pain.
