-SM Stirling, Against The Tide Of Years (New York, 1999), Chapter Fifteen, p. 230.
Exactly! You and I know what a bullet is but an ancient Assyrian doesn't so what will he think and how will he react? Recently in the combox, David Birr referred to a story in which a pastward time traveler killed his assailants with a gun. Witnesses thought that he held a hammer which invisibly flew from and returned to his hand...
When Stane tried to change history in post-Roman Britain:
"'None dared cross him, for he had a wand which threw thunderbolts and had been seen to cleave rocks and once, in battle with the Britons, burn men down.'" (Anderson, Time Patrol, p. 33)
Stane has "...a thirtieth-century blast-ray.'" (p. 36)
In Doctor Mirabilis, Roger Bacon believes that a gaseous explosion is demonic. In Black Easter, a scientist denies that a visible demon is real.
-copied from here.
A visible demon would be another matter.
I once heard (anecdotal evidence here, folks) that Australia aborigines said that a van was moved by "spirit horses." If they insisted on this explanation, then the phrase "spirit horses" would become the term in their language for "internal combustion engine."