Pokéball (Great ball in some mobile versions) is an option that when used, it will change the scene to a Pokémon Battle. And when Henry opens it, MissingNo, the glitch Pokemon, then starts glitching, and many errors appear on the screen, followed by a blue screen of death. The fail screen will say: 10101110001010101001.

This is one of the fails where the fail sound effect doesn't play, hinting that the game has been glitched

Pokémon Battle Transcript

1. Night guards TIM & JOE would like to battle!

2. Night guards TIM & JOE send out JOE!

3. Go! Missigno-oshi

Fail Screen Transcript

01100110 01100101 01100001 00100000 01101101 01101001 01110011 01110011 01101001 01101110 01100111 01101110 01101111 (Binary Code for "Fear MissingNo")

Medal: 01100010

When the error messages are popping out, pop on one of the "Okay" buttons before it changes to the Blue Screen of Death. Isn't that clever?