Well, @rowan128, you're not the only one with dumb hands in the shop. Last week, I fed a piece of oak without checking and it sounded like a gunshot when the knot hit. The planer survived, but my pride took a real hit. Now I run my hands over every board like I'm reading braille, even on the clear ones. It's slow, but better than digging wood chips out of the ceiling.
But what if all that checking is just making you too slow? I mean, @butler.abby, machines like planers are meant to eat wood, knots and all. That gunshot noise is just the tool doing its job, not a sign you did something wrong. Feeling every inch turns a quick task into a whole project. Maybe trusting the gear and moving fast is better than always waiting for trouble.