The Bloody Headcrab is famously known for the test map " boxing " where two headcrab zombies fight each other in a ring.
This version of the headcrab was first shown in E3 2003 which also came from the 2003 leaked beta. Unlike the standard headcrab it retains bloodstains everywhere on the front side of the headcrab. This version of the headcrab has more claws in the mouth area with the mouth being a bit smaller compared to retail.
They were to appear in maps like d1_town_01 - 05 as early Ravenholm maps (with similar maps). They only appear as zombies in those maps.
The design is very similar to the final version but has no blood in the frontal area. It also appears a bit smaller than the final version. It also has more detailed claws in the oral area.
The Bloody Headcrab Zombie version is based on the darkish blue-shirted Citizen with a more detailed open chest. The textures have also been moved to a singular sheet, and the mesh is in higher quality than others. This version of the headcrab has blue speckles on the bottom of the two legs which are far less prevailing in the final version. Unlike its older models this version does not seem to have a head but rather a boned jaw. The jawless head would be recycled for the Zombine.
Just like the Bloody Headcrab Zombie, it's whole model appearance,-even including the open chest part-and animations, retain in the final version. But just with a mostly reworked appearance via removing a majorly of the blood part, and improving its polygon count in both the retail version of Half-Life 2 and its episodes.