gistfile1.txt

    NSMutableArray *operations = [NSMutableArray array];

    [self.puppets.copy enumerateObjectsUsingBlock:^(AnswerKeyPuppet *checkedPuppet,
                                                        NSUInteger idx,
                                                        BOOL *stop) {
        
        [self.puppets.copy enumerateObjectsUsingBlock:^(AnswerKeyPuppet *puppet,
                                                            NSUInteger idx2,
                                                            BOOL *stop2) {
       
             [operations addObject:[NSBlockOperation blockOperationWithBlock:^{
                
                if (idx2 >= idx) {
                    *stop2 = YES;
                    return;
                }
                
                if ([puppet isEqual:checkedPuppet]) {
                    return;
                }
                
                if ([checkedPuppet isCollidingWith:puppet]) {
                    [self.collisions addObject:checkedPuppet];
                    [self.collisions addObject:puppet];
                }
             }]];
        }];
    }];

    for(NSOperation *o in operations) {
        [self.checkQueue addOperation:o];
    }