I breed staffs, I know when my bitch is ready for mating as my neutered OESD mates with her and sometimes they do lock! Its a great indicator as it means we never miss the right time, she has such long seasons and usually isn't ready till day 20+! Plus my poor boy gets a it of fun and always seems very proud of himself! I'm sure he thinks the pups are his as when they're born he's very paternal!
( Maybe she does too as she always lets him interact with them!)