To learn more, I called the veterinarian Larry Carbone, the director of the animal care and use program at the University of California at San Francisco. Policies in most countries call for easing or preventing pain or distress in lab animals whenever possible. Since the animals can’t talk, knowing how much discomfort they’re in to begin with “is really difficult,” Carbone told me. But over the years, researchers have devised good, standardized ways to measure reactions to painful stimuli in rodents and other animals. This might, for instance, include timing how fast a mouse yanks its paw away when you shine a hot light on it, and seeing how that reflex differs when a pain drug is administered.

More sophisticated tests track behavioral changes to gauge how much a painful situation bothers a rodent, Carbone said. For example, if mice in pain are given a choice between a chamber where their chow was laced with an analgesic, versus a chamber with regular food, they spend more time in the place that’s associated with pain relief. (Animals respond to many of the same analgesic drugs as we do.)

After rodents have undergone abdominal surgery in an experiment, researchers also can monitor for signs of pain (such as writhing or unsteady walking, or changes in burrowing or nest-building habits). Mice are highly motivated to build nests, Carbone said, and “we know if they’re in really bad pain, as much as they want a nice nest, they’re not gonna put the work into doing that.”

Still, scientists don’t have ways to measure animal discomfort or distress in all experimental contexts, including those causing chronic pain or anxiety. And it’s been controversial whether certain kinds of creatures—not just lobsters but also fish, whose brains are so different from ours—suffer from pain at all.

While most animals reflexively react to harmful stimuli (think of that hot light), that’s not the same thing as feeling pain and suffering, which are subjective experiences. “We can never know for sure” whether lobsters and fish go through that, says the biologist Hanno Würbel, who chairs the animal-welfare division at the University of Bern in Switzerland.

Still, he believes that recent studies make “a plausible case” that they do.

By law, research labs in the United States are supposed to assume that things that are painful to people are painful to other animals—including fish. The task of then deciding how much pain may be inflicted in experiments falls to a committee that oversees the care and use of animals at each research institution in accordance with the Animal Welfare Act and U.S. Public Health Service regulations and guidelines. These local committees approve or reject proposed study protocols, reviewing whether the pain or suffering in animals would exceed acceptable limits, or could be allayed by anesthesia or analgesics.