they adopt that posture so that they can produce the deadly silent fart. in order to varify that there is truly gas being passed, need a volunteer to put a lit candle there. if the flame flicker, it means there's wind, if there's flame thrown..... its definately gas
<object width="400" height="325"><param name="movie" value="http://www.youtube.com/v/s3HEGh328KY&hl=en_US&fs=1?rel=0"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/s3HEGh328KY&hl=en_US&fs=1?rel=0" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="400" height="325"></embed></object>