Crunch?

I’m not sure what it means but my baby also does that so I’m curious as well

I’m pretty sure this is a sign that they’re trying to sit up. It’s like one of the first indicators I think.

I recently saw a baby physical therapist make a video about this. She said that it's not that they're trying to sit up, but their upper abs are stronger than their lower abs. They're actually closer at this point to rolling than sitting up. She recommended to put something like a small cushion or bundled blanket under their legs while laying flat to encourage them to engage their lower abs and roll over

I saw something about it it is supposed to mean that their abdominal muscles are strong but that you should still help them learn to roll