Count the words of "the cat and the hat and the bat" with a dictionary.

The counts are {"the": 3, "cat": 1, "and": 2, "hat": 1, "bat": 1}.

The most common word is the, with $3$ times. The next is and with $2$.

Check. $3 + 1 + 2 + 1 + 1 = 8$, and the sentence has $8$ words. ✓