Back in the earlier years of Black Mesa, there used to be blood on your hands and weapons when you would kill someone/thing.
(NOT MY IMAGE)



This feature was later removed due to performance issues. But there is still a way to enable it. And it's a lot easier than expected.

To get bloody effects, open up the developer console and write "cl_mdldetailfx_enable 1" (without the quotation marks) and then simply kill something/someone.

Change "cl_mdldetailfx_enable 1" to "cl_mdldetailfx_enable 0" and the effects should be gone as soon as you load in the next map.

Thanks for reading and enjoy your weapons being covered by the blood of your enemies.