Mo doesn't explain how the lighthouse helps the sea serpent's toothache, but if you ever meet one with a similar problem, you might want to suggest one of the following, slightly more mainstream remedies to him:
1) Put an ice cube on the tooth (or the cheek closest to it) for 15 minutes, three times a day.
2) Crush some garlic and put it next to the affected tooth (Hippocrates' favourite cure- garlic tastes absolutely revolting raw, though!)
3) Drink some peppermint tea with a little salt in.
4) For the OVER 18s ONLY, rubbing whisky on your gums apparently works too.