I am 99 percent sure this was nothing more than my three year old messing around but my older Dd has (non epileptic) seizures which began at around this age so I'm probably more sensitive to things like this.
This morning Dd did a strange sort of snorting/growling noise then her arms sort of slowly flexed in an odd movement and her back did too. Hard to describe, she didn't respond to me when it was happening but did seem to remember it afterwards as she said it was a pig noise!
If it was some kind of funny turn or seizure she wouldn't remember would she? She seems fine since which again has reassured me as dd1 is always exhausted after a seizure. It also looked too slow and fluid for a seizure but was definitely a bizarre set of movements.