antenna - Oscilloscope Output with its positive terminal touching human's body and negative terminal left open

it once happened that when I touched the positive terminal of the Oscilloscope input probes letting its negative terminal open, I observed sinusoidal voltage signals with 0.5V peak to peak and of frequency nearly 50Hz. I don't understand the exact cause for these signals. When I touched the other, negative terminal output signal reached zero with a very little noise...(with the positive terminal connected to the body..) Is it because the power lines near the place I observed these are 50Hz and those induced a potential difference across me with respect to the supply ground which is also the ground of Oscilloscope... or something else.. When I touched a wire or a resistor with positive terminal of Oscilloscope.. there was no change in the Output.. Its because the equivalent model of our body includes capacitance and inductance with resistance.. If so then actually how we are being induced with such voltage signal..?
Actually the discontinuity in signal is because of the difference between the frequency of actual signal and sampling frequency of my camera.