Definition - What does Positive Displacement Pump mean? Positive Displacement Pump is a type of pump used to displace or force oil and petroleum products into pipelines or into various equipment installed in refineries.
A brain looks like a walnut because our minds are constantly making comparisons and finding similarities to help us understand the world around us. Here's an activity that can help you see more such things. Try to find faces.
Pecan halves also resemble what most people think brains look like. We could just as easily have decided to say brains looked like walnuts, except, people probably saw walnut meats before undamaged brains and thought the undamaged brain looked like a walnut.