my $var = 10;
print "There are $varapples";     # error: the compiler cannot know where the variable name ends
print "There are $var apples";    # OK: the space after the variable makes it possible to know that the variable ends just there
print "There are ${var}apples";   # prints: there are 10apples. 
                                  # A space is missing, but the print statement works, because the compiler can know 
                                  # where the variable name ends thanks to the curlies;