A.T. Robertson Commentary Revelation 13:3

"And [I saw] one of his heads as though it had been smitten unto death; and his death-stroke was healed: and the whole earth wondered after the beast;" — Revelation 13:3 (ASV)

And I saw (κα). No verb (ειδον) in the old MSS., but clearly understood from verse 2.As though it had been smitten (ως εσφαγμενην). Perfect passive participle of σφαζω, as in 5:6, accusative singular agreeing with μιαν (one of the heads), object of ειδον understood, "as though slain" (so the word means in seven other instances in the book). There is a reference to the death and new life of the Lamb in 5:6.

And his death-stroke was healed (κα η πληγη αυτου εθεραπευθη). First aorist passive indicative of θεραπευω. "The stroke of death" (that led to death). Apparently refers to the death of Nero in June 68 A.D. by his own hand. But after his death pretenders arose claiming to be Nero redivivus even as late as 89 (Tacitus, Hist. i. 78, ii. 8, etc.). John seems to regard Domitian as Nero over again in the persecutions carried on by him. The distinction is not always preserved between the beast (Roman Empire) and the seven heads (emperors), but in 17:10 the beast survives the loss of five heads. Here it is the death-of one head, while in verses 12,14 the beast himself receives a mortal wound.

Wondered after the beast (εθαυμασθη οπισω του θηριου). First aorist passive (deponent) indicative of θαυμαζω, to wonder at, to admire, as in 17:8. For this pregnant use of οπισω see Joh 12:9; Acts 5:37; 20:30; 1 Timothy 5:15. "All the earth wondered at and followed after the beast," that is Antichrist as represented by Domitian as Nero redivivus. But Charles champions the view that Caligula, not Nero, is the head that received the death-stroke and recovered and set up statues of himself for worship, even trying to do it in Jerusalem.