OH MY GOSH>>>>>>>>>>>>>>
I can't believe you asked this today....
Today I fed Cowboy celery for the first time and was HOPING it was OK, Celery is alot of water so i was thinking it was probably fine. I gave him small pieces and LONG pieces to crunch and play with . I put him in the pen with them and he ate half of the amount Iput in there which was equal to 2 stalks.
I didn't even think of filling them...good Idea
By the way...LOL.. He is still alive and kicking so I guess it was OK