Paula Patton's dog has a taste for human blood ... so claims a man who says her dog viciously attacked him and he suspects the dog's done it before.

Alberto Matiz is suing Paula claiming her German Shepard, Bear, attacked him on December 31, 2017 at Paula's Calabasas home. In docs, obtained by TMZ, Alberto claims the dog knocked him out and began ripping the flesh out of his right arm.

Alberto goes on to claim he thinks the dog's attacked others before. He's suing for unspecified damages.

Paula wished her dog Happy National Puppy Day just a couple weeks ago. She also told Conan O'Brien back in 2017 her dog had a tendency to run outta the house but always returned.