He video-taped the reactions of the squirrels, about 20 of which unwittingly took part in this experiment. The results were striking. Squirrels behaved with far more caution in response to larger, warmer rattles, as if they recognized the greater risk involved. In this case, the prey has developed the ability to assess its risks and act accordingly. Squirrels may use behavior like sand-kicking to probe for information, provoking a snake to rattle and, if you like, show its hand.
Snakes are physically unable to sound bigger or warmer than they actually are.
At least for now. But you never know. Evolution by natural selection came up with squirrels that could read a rattlesnake's rattle.