Does/did anyone else's baby ever put part of its fist in their mouth and move its head back and…

Does/did anyone else's baby ever put part of its fist in their mouth and move its head back and fourth? I'm a first time mom and I kinda worries me. My step son is autistic but when he gets excited he just shakes his hands really fast so I didn't know if what my baby is doing is normal or a sign of autism