Which animal sleeps standing up?

Some animals are able to sleep standing up. Notable among them are:

1. **Horses**: Horses usually sleep standing up, but lie down for deep sleep.

2. **Elephants**: Elephants sometimes sleep standing up, but they sometimes lie down.

3. **Giraffe**: Giraffes sleep standing up most of the time, although they sometimes rest lying down.

These animals stand on their feet while sleeping