Panel a: lateral CME speed along the southern flank as observed in STEREO-A and -B. The CME speed data points were extracted from the composite EUVI and COR1 images from 13:20 through 14:10 UT, at 5 min intervals. The CME reaches a speed of >1000 km s⁻¹ at 14:10 UT in both STEREO-A and -B. Panel b: faint EUV wave associated with the CME eruption, observed at the time of Sources 2 and 3. The EUV wave was only observed on the western hemisphere. The fast CME lateral speed after 13:55 UT (>500 km s⁻¹) and the presence of an EUV wave around the same time are strong indicators of a propagating shock wave surrounding the CME during the occurrence of Sources 2 and 3.