Big Brother is definately watching you.

CBP and DHS employs:

Advance Passenger Information System (APIS),
which provides:
Full name (last name, first name, middle name if applicable)
Gender
Date of Birth
Nationality
Country of residence
Travel document type (normally passport)
Travel document number (expiry date and country of issue for passport)
Address of the first night spent in the U.S. (Not required for U.S. nationals, Legal Permanent Residents, or Alien Residents of the U.S. entering the U.S.)

and Automated Targeting System
which provides
Date of reservation
Date(s) of intended travel
Other names on PNR
Number of travelers on PNR
Address
All forms of payment information
Billing address
Contact telephone numbers
All travel itinerary for specific PNR
Frequent flyer information
Travel agency
Travel agent
Code share PNR information
Travel status of passenger
Split/Divided PNR information
Identifiers for free tickets
One-way tickets
Email address
Ticketing field information
ATFQ fields
General remarks
Ticket number
Seat number
Date of ticket issuance
Any collected APIS information
No show history
Number of bags
Bag tag numbers
Go show information
Number of bags on each segment
Social Security information
Voluntary/involuntary upgrades
Received from information
All historical changes to the PNR

so if you get past this ...then I guess they are just checking to see if you have any vegetables or meat in your bags.