"You can make the blade from a spring leaf from an old Ford. We can grind it in Guanabacoa."
A leaf spring. Santiago says you can make a
Public DomainA leaf spring. Santiago says you can make a "killing lance" from one of the layers of the spring.

A spring leaf would be one of the metal layers of a leaf spring, "a composite spring, used especially in automotive suspensions, consisting of several layers of flexible metallic strips joined to act as a single unit" (answers.com).

Guanabacoa is a township in eastern Havana.

 

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