You can stick your tongue in it. Wouldn't recommend actually trying to get anything in your mouth.

You're protected by the thin layer of nitrogen that immediately sublimates, this lasts until the nitrogen heats up so the liquid can touch you directly, which you want to avoid.

For mostly the same reason you can stick a finger into molten lead (without losing said finger), provided you do it fast enough and your finger is wet enough.

You've never seen the trick where you put a small amount of liquid nitrogen in your mouth to demonstrate... science, IDK something to do with lederhosen?

Don't swallow it though, then you'll get a perforated stomach.