After spending five to six hours in the 'J' pose the monarch caterpillar attached by a cremaster, a hook-covered appendage that embeds into the silk pad. It twists around, deeply embedding its cremaster firmly in the silk. Then, it sheds its skin, revealing the chrysalis.
This shedding takes about 10 minutes - and I missed it three times - to reveal the chrysalis.

For reference - the head is at the bottom and the motion-blurred black lines were just behind the head in caterpillar form.

Some more details of what is going on here;

This process is driven by the hormone, ecdysone and works in conjunction with another hormone called the juvenile hormone. It’s actually the lack of the juvenile hormone that triggers the metamorphosis mechanism.

The juvenile hormone acts to delay metamorphosis throughout the whole larva stage. It works by blocking the genes in the imaginal discs — tiny disc-shaped bags of cells that kick into action when the caterpillar wraps itself in the chrysalis, eventually turning into an antenna, eye, wing or other butterfly bit. As such, the juvenile hormone is essential to the caterpillar’s survival prior to metamorphosis. Once the larva reaches its final moult and begins its metamorphosis, strange things happen to its body. Cells in the larva’s muscles, gut and salivary glands are digested and act as spare parts for the soon-to-be butterfly. Each cell is programmed to self-destruct through the activation of enzymes called caspases.

The caspases tear through the cell’s proteins, releasing prime butterfly-making material. Were it not for the juvenile hormone, this could have happened at any time, killing the caterpillar. Instead, nature programmed the hormone to lower its levels at the ideal moment for metamorphosis. With less juvenile hormone around, instead of inducing a regular moult, the ecdysone now drives the caterpillar to pupate. Once a caterpillar has disintegrated all of its tissues except for the imaginal discs, those discs use the protein-rich soup surrounding them to fuel the rapid cell division required to form the wings, antennae, legs, eyes, genitals and all the other features of an adult butterfly or moth. The imaginal disc for a fruit fly’s wing, for example, might begin with only 50 cells and increase to more than 50,000 cells by the end of metamorphosis.