The toxin in this episode is very similar to that of the Scarecrow, an infamous Batman villain.
This is the second time Lex Luthor's future is shown. First time the blind lady at the hospital had visualised the same turn of events when she had touched Lex's hands.
Lionel tells the prison warden that he is guilty of many crimes, but not the one for which he was convicted. That is a lie on his part as he confessed to Chloe in "Truth" while under the effects of the Levitas project; a substance that makes people answer truthfully. This is odd behavior for a supposedly repentant man.
Wendy Chmelauskas and Ben Odberg reprised their roles as Lewis and Laura Lang for Lana's hallucination. They were last seen in the Pilot episode.
On the Season 4 DVD set, there is an alternate dream sequence for Lex in which he dreams that he is about to get married. It is then revealed that the person he is about to marry is actually his mother, who starts to blame Lex for his brother's death and warns him that he is on a path to destruction. Lex responds furiously by strangling his mother before being woken up by Clark.