file handles return single lines in scalar context

while ( my $a =<DATA> ){
  my $b=<DATA>;
  my $c=<DATA>;
  print $a;
}

# while ( my $a =<DATA>, my $b=<DATA>, my $c=<DATA> ){
#   print $a;
# }
  
__DATA__
a
b
c
d
e
f
g
h
[download]

please note the difference, the second version will stop after printing "d", since the last group has only 2 entries (i.e. $c is undef)