Thanksgiving week is supposed to be a pretty laid-back affair — unless you’re preparing to fight the mobs during Black Friday, of course — but things got off to a rough start for citizens of Lochbuie, Colorado, on Monday, when an incredibly loud boom shook the town. Now, authorities and curious residents are trying to figure out exactly what caused it.

The strange happening occurred at around 9 pm local time, with countless residents of the small town not only hearing the incredibly loud bang, but feeling it. Those in the vicinity reported that their houses physically shook, rattling windows and giving just about everyone a scare. At the moment, there’s been no explanation for the boom, and the closest military base has said that there were no operations happening in the area at the time of the curious noise. However, some Lochbuie locals have their own theories.

The Lochbuie Police Department page on Facebook is packed with people proposing their own explanations for what caused the boom. Some suggest an aircraft sonic boom was the cause, but without military aircraft in the area that would seem unlikely, while others have wilder guesses ranging from an alien landing to an earthquake.