Apparently these facts upset some pet theory that he had long held in mind.

As it happens, I have a pet theory about that, too.

My pet theory is that this was the precursor event.

Procell was on a single track about his pet theory.

I don't know whether my pet theory would survive that test.

"Still," he said, not yet willing to drop his pet theory.

I've got my own pet theory about what's produced this period of calm - and, more important, why it may be coming to an end.

"Well, did you find any surprises in your pet theories?"

He warmed to the subject; this was obviously his own pet theory.

Now that your pet theories are being put to the test you're scared silly they won't work.