What happened to Rory and Niall?

One fine summer’s evening, Paddy, Mick, and Liam were riding back home from the bar, all three of them together on Paddy’s motorcycle. 

Of course, they get stopped by a cop.  

“Your motorcycle is only licensed to carry two people, and there are three of you,” he said, “one of you will have to get off and walk.” 

“Three of us?” asked Paddy, looking back in surprise at Liam and Mick.  “Jeez, what happened to Rory and Niall?”