[Aliantha]

From here:

as far as it will go into the cow’s rectum. Once his arm is all the way inside, the vet goes through a series of checkpoints to ascertain whether the cow is pregnant. He checks the position of the cervix and whether the ovaries contain fluid. The next step is feeling the embryo to determine its age.

It’s important for a vet always to wear a smile, even when his arm is deep inside a cow’s rectum.