That's what many people in the Alberta Rocky Mountain town of Banff were asking around suppertime Thursday.
"That" turned out to be a small earthquake, said Garry Rogers, a scientist with the Geological Survey of Canada.
The quake hit about 5:45 p.m. MT about four kilometres southwest of Banff and about 20 kilometres northwest of Canmore.
"It was a magnitude 2.7, what we would call a micro-earthquake, not a very big earthquake," Rogers said from Victoria, B.C.
"If you're right on top of it, it might be upsetting, but generally people in the region would just feel a mild shaking of just a second or two."
No damage or injuries have been reported.
Katie Kennedy was checking in guests at the Hidden Ridge resort on Tunnel Mountain in Banff when the temblor hit.
"It felt like a giant bowling ball going around, everything just started shaking," Kennedy said.
"It was pretty freaky though."
Banff Mayor Karen Sorensen had just got home from work and was sitting down for dinner with her husband.
"It sounded and felt a bit like a really large truck going by your home, but in my home I could feel it under my feet, it just kind of rolled through, two to three seconds, tops.
"I looked at my husband and said, 'what was that?'"
They immediately went outside to look around, and then Sorensen called her town manager, who called the fire chief.
She said the quake was felt all over town — her phone was constantly ringing, and she said social media was blowing up about it.
The mayor said she's been in Banff for more than 30 years and has never felt or heard of anything like this.
"I'm glad we're not dealing with damage or injuries and I look forward to understanding more about it," Sorensen said.
Earthquakes are rare in Banff, but several do occur every year in the Rockies, in places where there are no people to feel and report it, Rogers said.
He said there was a "quite sizable" earthquake just north of Banff in 1918 that was a magnitude 6.
At the end of August, a magnitude 6 quake in California near Napa, which sent 120 people to hospital and damaged wineries in the area.
— By Mary Jo Laforest in Edmonton