Molly draws a small hole halfway up the bottle, with the spoon pushed through below it for the birds to stand on.

She checks the first criterion: the hole is above the seed, so the seed stays in.

She checks the second criterion: the string at the neck holds the feeder on the branch, so it hangs by itself.

She checks the constraints: one bottle, string and one spoon, and she can build it in 40 minutes.

Molly's second idea meets every criterion and stays inside every constraint.

The idea meets every criterion and stays inside every constraint, so Molly keeps it.