Bubble Tip Anemones randomly swell up in sync

[Frost_Hydra]

I have these two otherwise happy BTAs (was originally just one that split a month ago) that randomly swell up. their base/foot looks like it just puffs as much as physically possible with loads of water, and the base of the tentacles seem to constricted like there's some invisible rubber band around them. The weirdest part is that this only lasts for around 2-3 minutes, but happens to both my anemones at the exact same time. I don't dose anything and I just happened to occasional see it happen when i'm just staring at the tank. After those few minutes are up, the anemones both go to looking perfectly normal again. Is this something I should be concerned about?

First picture is about 30 seconds after anemones began swellings, 2nd one is one in further detail, and 3rd is both after around 3 minutes and returning back to normal.

 

[Sk8r]

Mine (unsplit, but new) goes through gymnastics during the day, reverts by night to a little ball. My guess is that your set are just going through a growing process. They at least look healthy.

 

[Misled]

They are fine. When you get to twenty and they all do the same thing, just smile. They are funny little creatures.