It's actually not apple seeds by themselves. Apple seeds will pass through the digestive tract intact. However, the seeds contain amygdalin inside them, which w

It's actually not apple seeds by themselves. Apple seeds will pass through the digestive tract intact. However, the seeds contain amygdalin inside them, which will react into cyanide in the stomach. So what's toxic is chewing and then swallowing apple seeds. Peach seeds also contain amygdalin, although you're much less likely to try to eat one of those.