A slim cow is mother to a bull.
It means one who appears or looks weak may have strong associates, who normally would fight in his defense and so never should he be mistreated or manhandled due to his weakness.
Patois: Mawga cow a bull muma. Mi nuh like fi badda that old man deh caah him son a souljah
English: A person who appears weak may have strong associates. I don't like to trouble that old man because his son is a soldier.