I wrote:

...

The duo [of cats] watched the hole for over an hour, but the mouse never re-appeared. When they finally lost interest, I praised them for their vigilance and gave them an extra treat.

Hal Lane replied:

Are you sure that they don't think that you rewarded them for *stopping* their watch at the mouse hole? Behavior re-enforcement using rewards can be tricky...

If they got the wrong idea, they seem to have forgotten it. The duo was back at the hole a good part of today. Jim Muth