Perform the following tasks to unlock the corresponding sections in the "Secrets" area in the Tome of Knowledge:

HOW TO UNLOCK - SECTION
Type "celebrate" at the main menu - Lex dons a party hat and fireworks pop.
Type "elite" at the main menu - The tile grid will change to L33T letters.
Type "gobble" at the main menu - Lex dons a turkey tail and leaves fall.
Type "seattle" at the main menu - Lex gains a coffee mug and is rained on.
Type "winter" at the main menu - Lex gains a scarf, cocoa, and is snowed on.
Type "lovely" at the main menu - Lex is surrounded by hearts.
Type "moustache" at the main menu - Lex wears a moustache in-game.
Type "cone" at the main menu - Lex wears a road cone on his head in-game.
Type "pancakes" at the main menu - Lex wears pancakes on his head in-game.
Type "pirate" at the main menu - Lex wears pirate garb and giggles.
Click Lex in Adventure or Arena mode four times - Lex will giggle.
Click Lex in Adventure or Arena mode - Lex will hiccup.
Click Lex in Adventure or Arena mode eight times - Lex will sneeze.
Click an enemy in the Tome 6 times - Shows enemy's Death animation.
Click an enemy in the Tome - Shows enemy's Hit animation.
Click an enemy's attack in the Tome - Shows the attack's animation.

Unlock the following bonuses by performing the corresponding tasks:

BONUS - HOW TO UNLOCK
Adventure Replay mode - Complete Book 6 in Adventure mode.
Arena mode - Complete Book 6 in Adventure mode.
Mini-Games mode - Complete Book 5 in Adventure mode.
Tome Of Knowledge mode - Complete Book 4 in Adventure mode.