[erlang-questions] Why is the spawn_link not working?

[Yves S. Garret]

Hello,

I've recently created the following two modules from a book:
http://bin.cakephp.org/view/1356260281
http://bin.cakephp.org/view/13533081

Now, when I send Pid ! {moon, asdf}. I get the following output:
39> Pid ! {moon, w}.
Received the input and sending now.
Received the input to drop.
{moon,w}

=ERROR REPORT==== 12-Jan-2014::19:31:38 ===
Error in process <0.162.0> with exit value:
{badarith,[{drop,fall_velocity,2,[{file,"drop.erl"},{line,27}]},{drop,drop,0,[{file,"drop.erl"},{line,17}]}]}

Why am I not seeing this line run?
io:format("FAILURE: ~p died because of ~p.~n~n", [Pid, Reason]);
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