In some U.S.
states it is illegal to possess and/or carry such a knife in public. In
certain jurisdictions, butterfly knives are categorized as a "gravity knife
", or "dagger
" although they are also occasionally outlawed by name ("butterfly knife"). The knife is illegal in California
if blade length exceeds two inches. In a recent US Federal Court case,
Spyderco, Inc. pleaded guilty and was fined $75,000 for sending
butterfly knives through the United States Postal Service. Spyderco
admitted that from June 2005 through January 2007, it had mailed
butterfly knives, after importing the knife components from Taipei,
Taiwan, through the Port of San Francisco and the Port of Oakland, to
Golden, Colorado. 
You don't need a butterfly knife. Just go get a regular hunting knife. I have a few.