When the Vatican admitted it happened: Vatican spokesman Rev. Federico Lombardi confirmed reports of the head injury to the press just on Thursday.

Clues at the time: No reports mentioned any such injury at the time, but maybe that's why the pope had to wear that funny sombrero (we kid).

What it might have to do with his retirement: Father Lombardi says this incident "didn't impact" the pope's retirement decision, though Benedict himself has said that he's retiring due to health concerns.

Pacemaker

When it happened: Vatican officials haven't put an exact date on when Pope Benedict received a pacemaker implant to keep his heart beating normally, but they did say that he's had it since his time as a cardinal. That means he's had the pacemaker since at least 2005, if not earlier.

When the Vatican admitted it happened: This secret came to light Tuesday, when the Vatican also confirmed that Benedict underwent a secret operation to replace the pacemaker battery in December 2012.

Clues at the time: Speculation about the pope's health has come in fits and starts, with a Reuters story from April 2012 noting his new use of a cane in public. Benedict's brother talked with journalists about two minor strokes he suffered before his election in 2005, also citing his troubles with high blood pressure and arthritis. Still, when Italian journalist Antonio Socci floated the possibility of Benedict's resignation in late 2011, Vatican officials were quick to say, "The pope's health is excellent," making no mention of his pacemaker.

What it might have to do with his retirement: This seems to be the most likely reason as to why the pope is retiring — or at least the most likely reason he himself would give as to why he's retiring. In his 2010 book Light of the World, the pope gave readers fair warning that he planned to retire if his health ever kept him from his duties.

Construction of his retirement residence

When it happened: The pope has to have somewhere to go once he's officially an ex-pope, and thus no longer permitted to reside in the Apostolic Palace. We now know that preparations for his next home within the Vatican City limits began in the fall of 2012.

When the Vatican admitted it happened: Vatican spokesman Father Lombardi was cagey about this on Wednesday, telling reporters, "I don't think there was a consultation of the College of the Cardinals about this." But he didn't contradict reports in the Italian media that renovation of a convent where the pope intends to live after stepping down has been going on in secret for months now.

Clues at the time: This project was kept successfully under-wraps, though complaints last year from Vatican bankers about being overcharged for construction contracts may have hinted toward the work being planned within the Vatican City's walls.