to sting or bite (of mosquito, bee etc) / to say repeatedly / to urge insistently / to ask repeatedly / to stick to a point / (onom.) tinkling or jingling sound
叮
=
丁
+
口
:
In front of the engine ((e)ng1), Dorothy Gale (di) is celebrating the anniversary of the witche's death by repeatedly (叮) stinging (叮) a mandarin (口) with a nail (丁) and singing "叮咚 the witch is dead!"