This is a pun on 'feat' which in this context means an achievement that requires great courage, skill, or strength, but it's also being used because it sounds exactly similar to 'feet' which is what the spectators would actually be starring at if the walker was wearing diamond-laced slippers
The tightrope walker gently took a step at a time and always wore diamond - laced slippers . The spectators always would stare in awe at the tightrope walker ' s feat .