Back arching but not crying

[Danielle95lab]

Hey! So my son 4 months old has randomly started arching his back a fair bit when he's playing or sat in the bouncer etc. Seems happy and content, doesn't cry.. just wondering if anyone knows why he's all of a sudden doing it?

Can he roll from back to belly yet? I found my daughter was arching her back when learning to roll over.

No he can't, that might explain it! He has been using his legs to attempt to roll but that's as far as I've noticed. Then on occasion he just randomly arches his back in his bouncer and on the floor but doesn't seem in discomfort, so that could explain it! Thank you x

My 3 month old has just started doing the same thing! I'm pretty sure my older son went though the same phase and is just about them learning how to use their bodies. He arches and writhes about like he's trying to propel himself out of the bouncer. Looks odd but am sure it's harmless.