Attempted ipod theft, how do you react?

[glen]

So I am getting off the T today in Boston, As I do, I kind of trip on the cord and the music stops. Then I turn around and there is some 17 to 19ish year old kid with my ipod in his hand. He says, "just keep walking. . . " There are maybe 15 people in the T with me. He has 3 friends with him, all athletic looking, skinnyish but muscular. I immediately realize that this is more of an attempted theft that was botched, like he didn't think I would notice or something (despite the fact that the music would obviously stop). What is your first instinct as to how to handle this situation?