Final answer:
The interaction where vampire bats drink blood from cattle without causing harm would be classified as commensalism, which is a type of relationship where one species benefits and the other is unaffected.
Step-by-step explanation:
The interaction between the cattle and the vampire bat would be called commensalism if the bats drank blood but somehow caused no harm at all to the cattle. Commensalism is defined as a symbiotic relationship in which an individual from one of the species benefits while the individual from the other species is unaffected. An example that illustrates commensalism is the relationship between cattle egrets and large grazing mammals, where the egrets benefit from insects that are stirred up by the mammals moving through the grass, but the mammals themselves are not affected by the presence of the birds.