Problems with experiments using lab rats

I'm working on a story in which someone is trying to sabotage experiments. One possibility is to switch rats to confuse the results, another is to inoculate or feed them something that would cause a problem (infection, poison, or perhaps a drug). I'm not that familiar with how routine it would be for individual rats to be identified, vs. cages.

I'm also looking for some good ways for the researcher to get revenge on the saboteur and discourage future attempts. One possibility is that the rats become more aggressive after mistreatment or illness, and are more likely to bite. If anything is transmitted, it would need to be only to that one person. Rat bite fever, maybe?

Anyone have any thoughts on other possibilities that might make a satisfying end to the situation?

Thanks, Wendy, this is extremely helpful. That was my working scenario, identification by cage only but a suspicion of tampering based on recognition of a rat or two and change in behavior. Harder to get away with sabotage if the rats are individually identified.

The saboteur belongs in the lab. The idea would be to record tampering as a next step and to identify the person.

The last part is to figure out a suitable "getting his just desserts" to stop the tampering. Let's assume that the head of the lab has already made it clear that there's no interest in pursuing the allegations, and is disinclined to involve the police or fire anyone.

Thanks to all of you. A kiddie pool of paint sounds memorable, as do rats being used accidentally for two different experiments.

This is partly therapy, but with details changed and a reimagining of the ending of the situation. I've worked in several environments made toxic by sociopaths. One of these individuals was a researcher who escalated behavior to anonymous death threats and caused at least one person to end up in the hospital. In each case, the supervisors' response was to pretend the problem didn't exist or hope it would just go away. Requests for security cameras or phone recordings were denied as being of questionable legality. This type of situation is not terribly unusual, either, judging from other personal stories I've heard. There are also news stories on tampering with experiments that suggest the problem is underreported and usually involves, at best, trying to get either the saboteur or the victim of sabotage to go somewhere else.

As for using the tampered rats for revenge, the rationale is that the experiments are ruined already. I haven't come up with a satisfying way to end the story yet, but am thinking the rats might be expected to respond to aggressively to their tormenter, so when the tampering is repeated with switched-back rats, they bite. That might be bad enough, but if the rats also carry a disease, it might make the incident more serious.

Trying to put a stop to the tampering, combined if possible with some form of revenge, would be prompted by the saboteur not caring whether animals or people are injured or killed. Though the response is a bit desperate, it should end up short of murder--or for that matter, harming other animals.