We were watching wildebeest enter the river on the far bank and so missed the action unfolding below us.
This big croc grabbed a gnu that was leaving the water and pulled it back in and under. A massive splash alerted us and we were just in time to see the hapless wildbeest disappear back into the murky water. It happened too quickly for me to get an image so I waited and after about 5 minutes the croc re-surfaced with a lifeless gnu.