English is unusually lax by Indo-European standards in its rules on transitivity; what may appear to be a transitive verb can be used as an intransitive verb, and vice versa. "Eat" and "read" and many other verbs can be used either transitively or intransitively. Often there is a semantic difference between the intransitive and transitive forms of a verb: "the water is boiling" versus "I boiled the water"; "the grapes grew" versus "I grew the grapes". In these examples, known as ergative verbs, the role of the subject differs between intransitive and transitive verbs.