This is an odd question....

Today I happened to observe one of the cats digging a hole for the obvious purpose. It's in a disused part of our yard, so I didn't chase her away. She got ready to use it, then stopped, sniffed it, moved five feet away and dug a new hole, which she also rejected without even sniffing it this time. The third hole she dug, that's the one she pooed in.

I know why they bury it, but why did she reject her two previous holes?