I generally feed f/t ordered from a supplier, but for the few animals that I have that eat only live - I breed a few rats. On occasion I have had to serve p/k to my f/t eaters and about half of them won't take the p.k. (or live for that matter). If I stick the same rat in the freezer for a couple of weeks they take them readily. Yeah - I keep them on the same bedding as the ones I get from my f/t supplier - I called and asked. Go figure. I don't know what the difference would be - but they seem to be able to tell. Someone said that African Rats (which non-eating WC balls take readily)have no or very little scent - so I'm wondering if the freezing process helps to eliminate some of the additional smell of the rat? I don't know - just think aloud.
I'm sure you were thinking p/k would work better then f/t - maybe it does for some people - balls are funny like that.
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Tosha 
"Nihil facimus sed id bene facimus"

6.42.0 Ball Python (Harry and Fluffy and gang)
1.0.0 Angolan Python (Anakin Skywalker)
0.0.1 Green Tree Python (Verdi)
0.1.0 Bredls Python (Smurfette)
0.2.0 Feline (Pippen and Pandora)
0.0.1 Desert Tortoise (Pope John Paul aka JP )
2.2.1 Fish (1,2,3,4)
0.0.0 frogs rescued from pool skimmer
0.0.1 Lizard of unknown origin