Go through this story with your students to help them understand phrasal verbs and idioms regarding the word 'lay and lie'. Explain to them the differences between lay and lie. Talk about transitive and intransitive verbs. Transitive must have an object, for example, 'I lay my keys on the table'. The word 'lie' does not need an object so is intransitive, for example, 'lie down and go to sleep'. Lay is the past of lie and laid is the past of lay.