Exercise 1 solution

The reef knot lies flat and symmetrical: each end sits beside its own standing part. The granny knot looks lopsided and twisted, with the ends sticking out at an angle.
After pulling hard, the granny knot usually jams and can slip under load. The reef knot is usually easier to untie by pushing the two loops towards each other, but it too can capsize if pulled from the wrong direction.
Takeaway: check that each end sits on the same side as its own standing part.