Question: Is there any explanation to how Agent Coulson is alive even after Loki killed him in The Avengers?
Question: Can't remember which episode, but when Celeste is put back into her body, she has a French accent and speaks French, but in previous episodes in the flashbacks she had a normal accent. Am I missing something?
Answer: She was in a different body.
Question: How can Lizzie's father have died in the fire when in an earlier season, Red killed him in the hospital when Lizzie was already an adult?
Answer: The man Red killed, Sam Scott, was Lizzie's adoptive father, not her biological one. However, at that time Lizzie (and thus the audience), was led to believe her real father abandoned her and her mother, so expect more secrets to be revealed how her real father actually died (or if he's even actually dead).
Chosen answer: Coulson believes he was resuscitated then sent to Tahiti to recuperate. "A magical place," he calls it. But in the "Agents of S.H.I.E.L.D." episode "The Magical Place", Coulson, through a mind-reading machine, learns that he was treated by S.H.I.E.L.D. and a fake memory of Tahiti was placed as a "mask" of sorts over the painful memory of the operation, which involved a drug seemingly of alien origin to repair the damage, coupled with a lot of morally dubious surgery.