My shoe doesn't look like a duck in my closet, but it also doesn't look like the absence of a duck in my closet.

I'm not sure I understand this. Do you mean that the way your shoe looks is not evidence for the presence or absence of a duck somewhere in your closet?

I think the original quote was meant to imply that as long as your shoe doesn't have the properties that differentiate ducks from non-ducks then your shoe possesses the absence of duck properties and should be assumed to be a non-duck. In other words, for a given object each property must have a binary value for duckness and when all properties have non-duckness values, you should conclude that the object as a whole has a non-duckness property.

I get confused by too many negatives and ducks.