Jim Carlock said:

Width was less than .5 cm, or in inches about 1/8" wide.
The cuke was a foot or two off the ground, so not sure
how a slug could have gotten to it, but I imagine that's
possible. There are some small shelled snails outside but
those seem to remain on the ground sticking to the
bottoms of dead leaves and their shells are much bigger
than the hole.

That far off the ground it was maybe a slug or snail. They may
spend the day sheltering under leaves, but they come out at night.

--
Pat in Plymouth MI ('someplace.net' is comcast)

Any technology distinguishable from magic is insufficiently advanced.
(attributed to Don Marti)