Keep in mind that her encounter with "pouls" was spoken, not written. The "poux" warning probably came with a written note. Regardless, @bambax said she should

Keep in mind that her encounter with "pouls" was spoken, not written. The "poux" warning probably came with a written note. Regardless, @bambax said she should have known that, in a spoken context [lə pu] is the pulse and [lɛ pu] is lice. I argue that it isn't surpising that the author didn't have that knowledge. Lice exceedingly rare in adult life (if common for school kids). Pulse is specialized vocabulary.