What Causes the Amplitude Increase on an Oscilloscope When Touching the Lead?

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Hi PF, it's been a long time since I've posted on here. I have a lab due soon and it was regarding oscilloscopes. This isn't really a homework problem so I'm not using the template...

Anyways, when I held the input lead in my hand, the amplitude of the wave displayed on the screen got much larger. I can't think of a reason why that would be. TBH, I still don't fully understand the concept of the oscilloscope. I understand that it detects voltage and graphs it as a function of time. But where is this mysterious voltage coming from when I touch the lead? And why is it even a wave?

Thanks in advance for your help.
 
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You are surrounded by electromagnetic signals (at either 50 Hz or 60 Hz), due to the electricity powering the outlets in the room you are in.

Your body acts like an antenna for these signals. By touching the oscilloscope lead, this signal is displayed on the oscilloscope.
 
Thanks Redbelly. I suspected it had to do with some antenna affect. It's still confusing though... it's so hard for me to understand things when they're invisible.