This is a fanciful term for shocking things that feel like they're curdling your blood. Most often, you'll read or hear about a bloodcurdling scream, like an ear-piercing shriek. However, anything that fills you with horror can be described as bloodcurdling, like a terrible, bloodcurdling sight. Only terrible things are described as bloodcurdling, which means something similar to hair-raising and nightmarish. If something is only a little gross or disturbing, it's not quite bloodcurdling: this is a strong, visceral word.