How do I un-mute my headphones?

[Maz2Abz]

Mute Headphones

While taking my SE out of the case, I've managed to mute my headphones (but don't know how), how do I "un-mute" them without having to do a hard-reboot?

 

[Tartarus]

Mute Headphones

Did you press the volume up button and did you check if the switch on the side is in the mute position or normal position?
You could also see if your headphones or the phone speakers are selected in airplay.