Here is a another funny one, technically it isn't in HL2 but, it was a concept Idea for an opening to it from Rising the Bar. The Opening starts with you on a train heading toward c17 threw the wasteland, it describes a Gargantua standing on on the tracks by your train growling at it and then a...
Actually yes and no, they stabbed like that in the leak (I seen video) Also the Co-Op mod Obsidian Conflict has a working hydra.
The Hydra code is actually in the SDK files.