As you can see, it has sliced along axis 0, the first axis. A slice, therefore, selects a range of elements along an axis. It can be helpful to read the expression arr2d[:2] as "select the first two rows of arr2d."

How should you design your drills? That depends on the area you want to drill. Can it be easily isolated from the rest of your project? If so, try time-slicing, where you isolate one step in a more involved process and repeat the step until you’ve perfected it.