The holes are referred to as affordances, allowing fingers to be inserted. They are also referred to as signifiers, indicating where the fingers are to go to (Norman, 2013). Signifiers identify clearly how people discover possibilities: signifiers are signs, noticeable signals of what can be done (Norman, 2013). The different sizes of the holes give constraints to the limitation of the number of fingers to be inserted: a big hole suggests several fingers whereas a small hole suggests only one finger (Norman, 2013). The mapping between holes and fingers suggests the set of possible operations, and is signified and constrained by the holes (Norman, 2013). Furthermore, the operation is insensitive to finger placement in which the scissors will still work if you use the wrong fingers but it is not as comfortably (Norman, 2013).
Norman, D. A. (2013). The design of everyday things. New York: Basic Books.