I was playing on my Minecraft server and my hand was empty. I looked at the fence, but instead of mining it with my left mouse button, I accidentally pressed the right mouse button. Then I realized that if you have an empty hand and press the right mouse button and look at a fence, your arm moves, but nothing happens (like it's supposed to, but your arm is not supposed to move forward like you're mining). If it makes reproducing the result easier, I was playing in Creative mode, but I don't think this matters.