A very unusual hidden detail by Oda, being an easter egg character from another series!!
There are two Meltan Pokémon from Pokémon GO (which Oda has mentioned being a very big fan of) hidden in this panel.
Can you spot them both?
https://pbs.twimg.com/media/EY5f2CBWkAAlZm_.jpg
https://pbs.twimg.com/media/EY5gGVjWkAI_og-.jpg

ほんとにおって草