What is the padding with red substance inside of steak packaging?
That "padding" is an absorbent pad made of paper and plastic; the "red substance" inside is the juices (often mistakenly believed to be "blood") that have seeped out of the meat; the purpose of the absorbent pad is to absorb this liquid and keep the interior of the tray dry. Without it, the liquid would pool up and potentially spill out when the tray was opened or handled. Because the "red substance" came from the meat itself, no, it is not poisonous; the packaging is regulated to prevent toxic components from being used, so it too is not poisonous.