['x', 'Cats', 'Dogs', 'Frogs'],
    ['1900',   1,       11,           25],
    ['1910',   2,       5,         13],
    ['1920',   4,       13,           15],
    ['1930',   8,       3,         21],
    ['1940',   7,       17,           5],
    ['1950',   7,       5,         17],
    ['1960',   8,       11,           3]