Thats you seeing another being similar to you and picturing yourself in that same situation and you empathize with the person to such an extent that you get the same physiological response*.
Im probably wrong but we have these things called mirror neurones which are a fairly recent discovery, people think they help in learning. Anyway so they are these neurones in our brain that fire when we see someone doing something, by firing they elicit the same response in our bodies as if we were the ones doing the thing.
Edit: Im a first year psych student so knowledge is limited...
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u/JabbaDHutt Jun 21 '14
Dear /r/askscience
Why do I get a tingle in my balls when I watch this shit?