This device has recently appeared in canned beers in an attempt to
     mimic the taste and appearance of a true draught beer. It employs a
     small plastic bladder filled with a mix of nitrogen and beer at the
     bottom of the can. When the can is opened, the mixture is forced out
     through small holes in the bladder causing considerable turbulence at
     the bottom of the can. This results in a thick, foaming head of
     creamy bubbles. While not real ale (see next), this process does
     mimic the serving of beer through "swan necks" or "sparklers" and is
     the subject of much debate.