<span>In an event of a rattlesnake bite, keeping the person bitten to calm down is the 1st thing to do. When the venom reaches the heart of the victim, it could lead to a fatal death. So by calming down, the circulation of blood is prevented to rise. After which, they directly cut an "x" at the middle of the bite marks and suck out blood as many as possible hoping that the venom is also sucked out too. This was an old technique used in the Oregon trail and may not be the best technique there is nowadays.
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Drop in functioning, Unusual Behavior, and Mood changes. Just to name 3.
Photoplethysmography is used to track of heart rate during a workout
