Hi, other Mummies are right, is a comforting tactile touch.
Mine does that too. But after a while, babies change their habit to other stuff. For instance, mine like to do the constant rooting behaviour to a particular side...
For more info, pls read on head turning here:
http://m.raisingchildren.net.au/articles/body-rocking,_head-rolling_and_head-banging.html
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