In Chinese legend, the cicada is a symbol of rebirth. Since its shape and size are similar to the tongue, it was often placed in the mouth of the deceased to bring him back to life.
把這種有「復活」、「再生」寓意的東西，放在死者口中，象徵著盼望死者的靈魂，能脫離死去的軀殼，重新展開新生命。加上蟬的形狀大小和舌頭相近，正好放入口中，用以壓舌。