Tonight, 12/6/12, I flew to MYR to see family on NKS347. As we pushed back (6.14pm for the scheduled 6:30pm), the flight attendants were doing the safety demo. Suddenly, the aircraft bounced, jerked to the right, and stopped short. The flight attendant in the rear galley got thrown a bit, and even had to stop in the middle of the safety demo after ending with an "Ouch!", so she must've gotten thrown or shifted a good bit. After about two minutes, the safety demo was continued, by the same flight attendant. After the safety demo had bad done, about 3 or 4 trucks approached the aircraft (The orange-lights ontop made me assume they were mainence trucks). After another 5 or so minutes, we (slowly) continued our pushback, after the maintenance trucks dispersed. I don't know what exactly happened, but it almost felt like we had run something over.
Does anybody at LGA have any ideas as to what may have happened?