A glitch emote bubble above Red's head
Glitch emote bubbles are glitch 16x16 graphics that can be seen above an NPC's head. All emote bubbles appear to wrap around every 0x30 entries, meaning emote 0x30 would be the same as (valid) emote 0x00.
Examples of valid emote bubbles are the "!" mark, "?", smiley face (Game Corner) and the Yellow exclusive walking Pikachu emote bubbles.
To view them, use Pokémon Red and Blue Game Genie code and use a Game Corner slot (requires a Coin Case and coins):
Where XX is any value that is not 00-02
The equivalent Game Genie code for Pokémon Yellow is:
Where XX is any value that is not 00-07