A twist bends the strip between two slices into a saddle; its normal came
from one corner's triangle, which leaned so far back that from about 60° of
twist every wall was taken for facing away and dropped, leaving the front
cap alone. Each strip now takes the whole quad's average normal (Newell's),
as Inflate's facets do. A test checks the faces kept against each strip's
average normal oriented away from the axis, for twists up to 300° and four
views.