make sure to keep your mouth open and your teeth far enough apart that the blade or tongue (moving part) has room to pass between
your teeth as it vibrates...avoid dental work

http://en.wikipedia.org/wiki/Jew%27s_harp

http://www.davidholt.com/music/playjawharp.html - David Holt's tutorial

if a picture is worth 1,000 words, how many is a moving picture worth?
http://www.youtube.com/watch?v=Ddhb8oKoWmon - jaw harp heaven

http://www.youtube.com/watch?v=yx0nnZZVnd8 - appalachian style

there is actually a festival...http://www.youtube.com/watch?v=6LMrSgRgiEk&feature=related

http://www.youtube.com/watch?v=23kzXRaosyA&feature=related
auld lang syne

Buffy St. Marie plays mouth bow on Pete Seeger's t.v.show
http://www.youtube.com/watch?v=krx2MoTaAVo&feature=related

http://www.alashensemble.com/instruments_xomus.htm
in Tuva this type of instrument is called xomus of khomus
http://www.youtube.com/watch?v=pIFgGveeF84

and in India..
http://www.youtube.com/watch?v=MnMXzCGNPSo&feature=related

Kyrgyzstan...
http://www.youtube.com/watch?v=OPTWQnEMEjg&feature=related

there is also a video from Brazil (or Portugal)
they are also popular/common in Scandinavian Norwegian music.