Bhikkhu Khantipalo's translation is:
“I undertake the rule of training to refrain from killing living creatures.”
It is a Pacittiya
confession offence for a monk to intentionally kill animals or insects. So it is not the end of the world if you intentionally kill some headlice. I don't know what the kammic gravity is though.
Yes the precepts are not for status looking down on non-Buddhists but are working on a skill: killing is never skillful, stealing is never skillful etc. (see Getting the Message
by Thanissaro Bhikkhu).
The precepts are for the purpose of concentration and freedom from remorse which naturally leads step by step to Awakening (See AN11:2
I am memorizing the Ahina Sutta
: By a Snake which is a metta chant to ward off dangerous creatures. I'm confident this will reduce the risk of getting headlice.
I thinking I'm worrying too much about hypothetical situations. Thanissaro Bhikkhu wrote in Precept Meditation
to set up the intention to keep the precepts and then be alert to actions that go against that intent. This would include mental actions like aversion for headlice.
A Tibetan teacher said that the prerequisite for human rebirth is good moral discipline saying it is almost a miracle that we've received it given how hard it is. I interpreted her as referring to perfect sila. I am a bit of a perfectionist.
Thanks for listening,
With metta / dhammapal
PS I just had a brilliant thought! I can sincerely undertake the rule of training to refrain from killing living creatures because it might not be for many years into the future that I have the misfortune of getting headlice by which time I might have successfully trained to become more like a Bodhisatta.