@a = qw( a b c );

+---+---+---+---+
| a | b | c | / |      / = allocated, but unused.
+---+---+---+---+

push @a, 'd';

+---+---+---+---+
| a | b | c | d |
+---+---+---+---+

push @a, 'e';

+---+---+---+---+---+---+---+---+---+---+---+---+
| a | b | c | d | e | / | / | / | / | / | / | / |
+---+---+---+---+---+---+---+---+---+---+---+---+