My 8 month old son tenses up by straightening his body, making himself stiff and doing a little grunt type noise. His legs go straight and stiff. It happens a lot during diaper changes but also sometimes when he’s playing on his back the floor.

He’s done it since he was very young, multiple times a day. Once he did it in front of a nurse and she said it wasn’t a seizure but didn’t say much else.

Did/does anyone else’s baby do this? Is it normal?