Besides, he never moves forward until he has fixed his thread to the ground.

With this support to his feet, he has no falls to fear, no matter what his position.
I had a proof of this before my eyes during a whole week.

As I have already said, the track, instead of keeping on one level, bends twice, dips at a certain point under the ledge of the vase and reappears at the top a little farther on.

At one part of the circuit, therefore, the procession walks on the lower surface of the rim; and this inverted position implies so little discomfort or danger that it is renewed at each turn for all the caterpillars from first to last.
It is out of the question then to suggest the dread of a false step on the edge of the rim which is so nimbly turned at each point of inflexion.

The caterpillars in distress, starved, shelterless, chilled with cold at night, cling obstinately to the silk ribbon covered hundreds of times, because they lack the rudimentary glimmers of reason which would advise them to abandon it.
Experience and reflection are not in their province.