At 10 months, some infants will begin to repeat back words they hear, although they may not yet know that these words have any particular meaning. They may not repeat these words completely or accurately, because many sounds are difficult to make for children at this age. For example, "hat" may be spoken as "ha" without the final "t" sound. By 17 to 21 months, verbal imitation is much stronger and more frequent than physical imitation (copying actions they see).