Subject 67 is a paper note in Fallout 76.
The note can be found in AMS corporate headquarters, in the Animal Holding area. It is behind a locked door that requires either Hacker 1 or Picklock 2 to open.
Subject 67. Cow. Exposure to heated Ultracite. Double standard dosing.
Observation: Growth of a second head. No loss of function.
Conclusion: Ultracite exposure still consistent with advanced radiation mutations.