How to tell if acans are opened or closed

[Deadlocked]

How do you know if an acan is open? Ive seen their sweeper tentacles, but im not sure what a closed acan looks like. Other corals are much more obvious. Thanks in advance.

 

[helmsreef]

They will close up like blastos when they are fed or not happy if that helps at all

 

[KK's Reef]

If they're closed, it's obvious. Their flesh recedes into their skeleton and they'll look shrunken in. When they're happy, they look fleshy and have a gentle sway in the current.