Trying to understand nodes

[jimhanus]

Can someone explain to me how nodes are created? If I draw a wavy line with the freehand tool, there is a node at each end and nodes created in the middle. I can try to duplicate the line several times as precisely as possible the nodes along the line will be in different places. If I draw any curved line as smoothly as possible the nodes still appear at different points, and not where I expect them to be. Could my mouse be causing the nodes as I draw without my knowledge? The attached file shows what I'm asking about. Note the 2 nodes at each end, I don't understand why they appear where they do. I never know what I'll end up with until I stop drawing. On the second file I would expect the node to appear near where the arrow is, but one appeared at the other end instead. Please enlighten me!

Jim