In this clip Vasso and Cat demonstrate the common artefacts during EEG recordings. It is important to critically evaluate the data you've recorded. In the worst case it could have just been muscle activity. See the plot below which shows EEG from the forehead relaxed and smiling.
The positive electrode was placed at Fp1, the negative at A1 and GND at A2. Same setup as shown in the video clip.
The first two references describe the EMG contamination of the EEG and then the following references discuss how this contamination affects brain computer interfaces and depth of anesthesia monitors (bispectral index). Both applications can be fooled into taking EMG for EEG with quite disturbing results.
Next clip: Using dry EEG electrodes.