The baby will wake up and cry when a pacifier falls out from the mouth. You may have to put it back in his mouth for him to sleep again. However, if the baby does not wake up, then there is no need to put the pacifier back. Also, do not remove a pacifier from the mouth of a sleeping baby. It may startle him and disturb his sleep. Do not attach a pacifier to a baby necklace or toy to prevent it from falling while the baby is asleep. A string or toy can increase the risk of suffocation.