Their first poop doesn’t stink.

The black, tar-like stuff called meconium is made up of mucus, fluid from the womb, and anything else they digested while inside mom. But it doesn’t yet have the gut bacteria that make poop smelly. As soon as you start feeding a baby, bacteria will start colonizing their intestines. After a day or so, bowel movements become green, yellow, or brown — with that familiar odor.

Sometimes infants stop breathing.

Likely when they’re sleeping, they may pause without a breath for 5 to 10 seconds — just enough time to make a new mom or dad panic. Irregular breathing is normal. (But if your baby stops breathing for a longer time or turns blue, it’s a medical emergency.) When babies are excited or after crying, they may take more than 60 breaths in a minute.

They can scare themselves.

It doesn’t take much to startle a newborn: a loud noise, strong scent, bright light, sudden motion, even their own cries. You’ll know it’s happened when he flings his arms out to the sides, hands open, then quickly closes up and tucks back in toward his body. This Moro reflex might have developed as a warning signal that a young monkey was off-balance, so mom could prevent a fall.