Charles H. Spurgeon on Psalms 141:5

It shall be an excellent oil. Certain oils are said to have a most salutary effect on the head; hence in fevers, or any other complaints which affect the head, the medical men always recommend oil. I have known people who were deranged, cured in a very short time by nothing more than the application of a peculiar kind of oil to the head. There are, however, other kinds which are believed, when thus applied, to produce delirium. Thus the reproofs of the righteous were compared to "excellent oil", which produced a most salutary effect on the head. So common is this practice of anointing the head, that all who can afford it do it every week. But, strange as it may appear, the crown of their heads is the place selected for chastisement; thus owners of slaves, or husbands, or school masters, beat the heads of the offenders with their knuckles. Should all urchin come late to school, or forget his lesson, the pedagogue says to some of the other boys, "Go beat his head!" "Begone, fellow! or I will beat thy head." Should a man be thus chastised by an inferior, he quotes the old proverb: "If my head is to be beaten, let it be done with the fingers that have rings on"; meaning a man of rank. "Yes, yes; let a holy man smite my head! and what of that? it is an excellent oil." "My master has been beating my head, but it has been good oil for me." —Joseph Roberts.