Abdul Baha : "He needs a slap."
One time, [‘Abdu’l-Bahá] took an oath, “By God, besides Whom there is no other god! I will appear with the perspicuous serpent.45” When He spoke that oath, my father, Ustád Abú’l-Qásim, was in His blessed presence and was so thrilled and overjoyed on hearing this that he kissed both blessed shoulders [of ‘Abdu’l-Bahá]. His meaning by “perspicuous serpent” was the blessed person of the Guardian of the Cause of God, who, like a dragon, destroyed and obliterated all the Covenant-breakers.
One of the inhabitants of ‘Akká was exhibiting great opposition. ‘Abdu’l-Bahá stated, “He needs a slap.” Next day that person died. It was said to His blessed presence, “He received his slap,” but He did not respond.
Ref. : With ‘Abdu’l-Bahá - Reminiscences of Khalil Shahídí, translated by Ahang Rabbani, Page 41