I had a feral that was particularly fertile. Before she got TNR'd she had so many kittens that she would bring them out early for me to start feeding because she couldn't. She was so angry when she got caught in the trap to go to the vet. But after I picked her back up, kept her the required overnight and then released her the next morning she turned at me and gave me the most hateful look. But inside that look was another one in her eyes. They were saying "I know what you did and thank you so much!" She was grateful to never have to get PG again.