It also raised one of the biggest questions:
How can you charge someone with accepting a bribe but charge no one with giving it?
"It's not common. If you're going to go after somebody for receiving a bribe, you would think that it is of equal importance to have the person offering the bribe involved," Ottawa criminal lawyer Lawrence Greenspon told the CBC.
While it may not be common, it's certainly not unheard of. And a clue to the answer lies in the text of Section 119 of the Criminal Code of Canada. That's the part that deals with bribing public officials.
The section says that for a crime to be committed, someone needs to "corruptly accept" or "corruptly give" something of value.
"One has to look at each side of the equation separately. In other words, in either case what's the legal requirement essential to the charge is a corrupt intention," former House of Commons Law Clerk Rob Walsh explained on CBC's Power & Politics.
"It's the corrupt intent that lays the foundation for a bribery charge," added Daniel Brown, Toronto region director of the the Criminal Lawyers' Association.
Brown says the implication is that the RCMP believed Duffy was the only person with a corrupt intent. That said, Brown's not convinced.
"It seems as though his intent of receiving the payment was to pay back the government and so it wasn't clear to me what his corrupt intent would be."
Prime Minister Stephen Harper's former chief of staff Nigel Wright has said he gave Duffy $90,000 to ensure that the Canadian public was not left out of pocket for Duffy's expense claims.
The RCMP, which said Wright "gifted" Duffy the money, announced in April that Wright would not face charges.
Why bother with a charge of bribery
So why pursue the charge against Duffy?
Brown suggests the answer to that question might lie in the RCMP's own insecurities.
"The RCMP are certainly concerned with being accused of playing partisan politics," argued Brown.
"They want to ensure that everything appears to be above board. They don't want to be criticized later on for not having laid charges where evidence may have existed," he added.
The evidence behind the RCMP decision to charge Duffy and not Wright may be revealed in court later.
Or, maybe not. Walsh wonders if the laying of the charge could have something to do with the other 30 charges.
"As you know, plea bargaining is part of the justice process and 31 charges is a lot. I think Sections 119 [bribery] charges and 121 [fraud on the government] are doubtful. They could be dispensible," said Walsh.
In Walsh's opinion, Duffy has a lot more to worry about on the fraud and breach of trust fronts. Those are all the charges that have to do with housing expenses, per diems and questionable contracts.
So how does Duffy defend himself against bribery?
Brown said he'll use the Nuremberg defence - the "I was just following orders" defence used by Nazi officials on trial for war crimes between 1945 and 1946.
"What he's doing is mounting a defence that he was just doing what he was told to do. That he was essentially forced into this plan to repay the money. He was ordered to do that at the request of the prime minister or the Prime Minister's Office," he explained.
Regardless of whether the bribery charge sticks or how Duffy plans to defend himself, the once-jovial senator from P.E.I. says he is eager for his case to be heard in court.
Outside his residence in Cavendish, P.E.I., he told the CBC this:
"I'm keen to have my story heard by Canadians in a court of law where people are under oath. When that story is finally told, Canadians will understand that I have not breached the Criminal Code of Canada."