A line of iambic pentameter comprises five consecutive iambs. In English accentual-syllabic verse, iambic trimeter is a line comprising three iambs. Also, the third anceps of the iambic trimeter line must be short in limping iambs. He uses hexameter that mixes iambs and anapests. The metrical feet used in the poem are a mixture of anapests and iambs. Note that Shakespeare does not rigidly follow a pattern of five iambs per line. He intersperses anapests and iambs, using six-foot lines (rather than four feet as above). The first two lines actually contain anapaests in place of iambs. However, any line mixing iambs and trochees could employ a cretic foot as a transition.