"Because their words had forked no lightning they" [___]

The line has ten syllables: “Be-cause their words had forked no light-ning they.” Ten syllables can form five iambic feet, each with an unstressed syllable followed by a stressed one: “beCAUSE | theirWORDS | hadFORKED | noLIGHT | ningTHEY.” That makes the line iambic pentameter, not tetrameter, which has four feet.

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