The Lepidoptera hominid molts into the adult form. With real butterflys and moths, there are generally five instars, four moltings, of the larval, or caterpillar stage. With each molt the larva gets bigger but retains the same basic shape. Then the insect becomes a pupa. During the pupal stage the insect's body is completely rebuilt into the adult form.
This is a recap episode; a significant number of the scenes are flashbacks using footage from previous episodes. Recaps, and bottle episodes, like season1 Requiem and season2 Next Tuesday, are faster and cheaper to make than regular episodes. It is not uncommon for TV shows to use a bottle or recap episode in the second half of a season to free up resources for an impressive season finale.
Peter DeLuise, who plays Ernie Watts in this episode, worked on Stargate SG1 with Amanda Tapping, as well as several other members of the DeLuise family. Peter is also a regular director of both series, including this episode.
For a knockout gas Henry is going to use 'dimethylchloride'. This gets weird. Methane is one carbon with four hydrogens tacked on. You can replace one or more hydrogens with chlorine, but you can't have more than one methyl for one chlorine. A two carbon molecule with six hydrogens tacked on is ethane, which with a really twisted misuse of language could be called dimethane. Ethyl chloride is a known anaesthetic.