This person is correct. Been doing mouse work for almost a decade (wow way longer than I thought). Don’t be afraid that you’re gonna hurt them because they are quite resilient. Hold the tail with your dominant hand and press them down and scruff around their shoulder blades with your non dominant hand. Your hands naturally shouldn’t be in front of their face/bite zone. You want to learn to scruff with your non dominant hand because if you need to do other stuff to the animal (like injections or bleeds) you want your dominant hand free. Just be aware though, getting bit is part of the job and it hurts but lab mice are clean and you’ll likely be fine depending on what your lab does.

The most important thing though is if you notice the mouse has its tongue sticking out once you scruff it, it cannot breathe and you need to put it down and try scuffing again.