A pin's brass.

It might have verdigrease on it." "What's verdigrease ?" "It's p'ison.

That's what it is.

You just swaller some of it once -- you'll see." So Tom unwound the thread from one of his needles, and each boy pricked the ball of his thumb and squeezed out a drop of blood.

In time, after many squeezes, Tom managed to sign his initials, using the ball of his little finger for a pen.