You can take a screenshot on a Macbook by pressing Cmd+Ctrl+Shift 3.
A quicker solution than pressing all those keys would be to:
Go to the FeralHeart login screen > Options > Controls > Scroll all the way down to the 'Print Screen' option > Press change and replace 'Prnt Scrn' with any character that is not already used to trigger anything.
I've did this with the f3 button and I've replaced it with the letter O.
For some reason my Inspiron won't let me hit my f keys with FeralHeart open.
This is just a quick, easy fix. ^^