Regex for test strings with only letters

I have a form input which is where I only need to take speakable text phrase ( i.e no numbers, symbols etc )

I’m using following Regex pattern to test the user inputs.

const friendlyPhraseReg = new RegExp(/^[aA-zZs]+$/);

friendlyPhraseReg.test('@@') // false

friendlyPhraseReg.test('11') // false

friendlyPhraseReg.test('%%') // false

friendlyPhraseReg.test('&&') // false

friendlyPhraseReg.test(')')  //false

friendlyPhraseReg.test('"')  //false

friendlyPhraseReg.test('/')  //false

It all make sense until I try to test following two strings

friendlyPhraseReg.test('\') // true
friendlyPhraseReg.test('^^') // true

Why does it only return true for ‘^’ and ” ? I’m not very good with regex so pardon me if im asking a stupid question. Can someone clear me why its return true only for those two symbols ?