If they're too shallow, they'll ricochet off the atmosphere like a rock skipping off a pond.
6 seconds sound clip from the Apollo 13 movie soundboard.
You can hear this line at 01:40:08 in the Blu-ray version of the movie.
Quote context
[...]
- Can they fly it manually and still shut it down on time without the computer?
- I guess that's the best we can do. We're out of time.
- If they're too steep, they'll incinerate in the steadily thickening air.
- If they're too shallow, they'll ricochet off the atmosphere like a rock skipping off a pond.
- Okay, people, on your toes. We're doing this one blind.
- Look, it will ignite, will it not?
[...]