Google does not allow "stemming" or "wildcard" searches. Thus, a search request for "baboon" will not find pages using only the plural "baboons." The best approach is to add both "baboon" and "baboons" (without the quotation marks) to the "At least one of these words" input box.
Google is not case sensitive. To Google, "BABOON" is the same as "baboon." For more information about creating effective search requests using Google, go to: Basics of Google Search or Advanced Google Searches.