it's sensing everything. so the fact that we got a ping tells you a good place to go with the "ocean shield" to start looking deeper. >> professor stupples, how is the listening technology on these buoys different than what the ship is using to pick up the pings? >> well, the towed ping locator is very much more sensitive than this bouoy. the buoy contains a hydrophone. that is not to say that it hasn't picked up a ping from the locator. >> and david, the big question now, investigators have said these signals have the potential of being from a manmade source. >> uh-huh. >> i think we agreed last night that it's hard to imagine what they could be other than the black boxes. but what could it be? >> well, the only thing that i looked -- i did research to try and find out. the only thing i found out was