Your functions and blood are all moving by the force of gravity, so when everything is raised or lowered(moving your arm), your pulse wave changes. This can also result from subtlty in higher blood pressure, when activity occures. Just as your pulse waves changes in the rest of your body when excersising, you will have a slight change in pulse when simply moved your arm up and down, you're gettin' that blood pumping! ;)
First, because you need to be careful of what you are eating and should not eat. Second, if you don't care about what you eating it could be really dangerous.
