A series of photos published Monday show a male lion pulling a tranquilizer dart from his companion’s shoulder at the Ol Pejeta Conservancy in Kenya. The lion was darted by a team of park rangers working for the Kenya Wildlife Service, who were reportedly subduing the animal to check her health and fit her with a radio tracking collar for further study. During the process, they treated her for a wounded paw.

The photos reveal an uncommon behavior for the lions, so we asked Luke Dollar, a biologist and the program director for the National Geographic Society’s Big Cats Initiative, to help us make sense of it. He took a break from working with lions in Zambia