Q: Context: Daley first made three guest appearances as Sweets during the first eight episodes of Season 3, first appearing in "The Secret in the Soil". He was promoted to a series regular and appeared in the opening credits beginning with the episode "The Santa in the Slush". He also guest-starred on the spin-off The Finder. The character is killed off in the first episode of the show's tenth season, "The Conspiracy in the Corpse", making him the first main character of Bones to die.

Question: when does dr sweets first appear on bones? Let's give stream of consciousness first:
To answer this question, we should know that: Daley first made three guest appearances as Sweets during the first eight episodes of Season 3, first appearing in "The Secret in the Soil". Therefore, the final answer is The Secret in the Soil.