Bearded Irises bent stalks

Are bearded iris stalks affected by cold night temperatures? After last week's very warm weather I had loads of bearded irises standing up straight with buds ready to open. Then on Saturday night we had a frost and on Sunday most of them were all bent over and twisted, but otherwise healthy and some with flowers. I remember it happening last year but I can't remember if it was weather related and whether they straightened up again or not. Can anyone shed any light on it?

 

What do you mean "or a cat" Andy?

 

I doubt it Andy! Next door's cat does come into our garden, and is quite welcome, but he'd have a job to sit on such tall stems, and so many of them in one night! Unless it was a whole pack of meerkats!