Why does the 'amazon-ecs' gem return no results when the search string is too detailed?

Question

I'm trying to pull search results from the Amazon Product Advertising API (amazon-ecs) gem. I am having issues with my search string, but only when it is too detailed.

Now assume that a user enters this search:

 search_string = 'big book of birth'

In that case, this works:

 res = Amazon::Ecs.item_search(search_string, {:response_group => 'Large', :search_index => 'Books'})

In other words, in my console I get the following:

 res.has_error?
 => false

Even this works:

 search_string = 'big book of birth by'
 res = Amazon::Ecs.item_search(search_string, {:response_group => 'Large', :search_index => 'Books'})

 res.has_error?
 => false

Mysteriously, this DOES NOT WORK:

 search_string = 'big book of birth by erika lyons'
 res = Amazon::Ecs.item_search(search_string, {:response_group => 'Large', :search_index => 'Books'})

 res.has_error?
 => true
 res.error
 => "We did not find any matches for your request." 

Is there some options / param that I need to include to make this search "fuzzy" like the one on Amazon.com (e.g., spellchecker, truncating unnecessary words, etc.)? There, searching 'big book of birth by erika lyons' results in the exact book at the top of the list after truncating some words.