Half a Bladder?

I get strange messages on my answering machine. It's happened since I've lived here. Very few of them are directed toward me and I sometimes feel like some kind of unwitting spirit medium for the phone age. This one from last night:

Robbie, did I say "half a kidney, or half a bladder?". It's "half a bladder". OK mate? Sorry about that if I made a mistake. Bye.

Thing is, I'm trying to work out a context in which this would make sense, but I just can't. Half a bladder? Half a kidney? Here, listen to it yourself and help me with this metaphysical telecommunications conundrum:

[Link] - mp3 file.