Why do babies arch their backs and throw their head back when they're upset?

Other than crying this is the other way where they use their body to express themselves since they can't talk get. Even toddlers do this at times. You need to find out what is the issue that is causing distress to him but usually it's loud noise, overtired or just wanting your attention. You can calm baby down by cuddling and talking softly to him or try walking him around in your arms. Sometimes touch doesn't work then you may have to put your baby on a mattress or bed and let him sort it out on his own. http://www.babycentre.co.uk/x1048721/is-it-normal-for-my-baby-to-arch-her-back-and-throw-herself-backwards-when-shes-upset