Found this little glitch... If you shoot-down a basilisk over deep water, it drowns instantly (that's epically cool), but there's also a sound glitch... The monster keeps playing the ambient sound that you hear while it's alive, so you continue to hear snorting, sniffing and growling even though it's stone dead and bobbing in the waves. :)

Found the perfect spot to re-create this bug...

On Skelige's main island, fast-travel to Fornhala. To the East of the signpost there's a watery/swampy area, and in the middle of it is a rather large dead tree with a cockatrice flying around it. Water is EVERYWHERE around the tree, and most if it is deep enough to drown the critter in, so even if you don't have the best timing with the crossbow, it's still pretty easy to crash-land it in water... At which point you'll notice that the dead beastie continues to play it's ambient monster sounds... ;)