Set fire to a geoduck if you want to annoy it. Fire won't kill a geoduck, but have you ever been on fire? It's not really pleasant. So you'll just annoy it pretty badly.
You know who loves annoying geoducks more than anyone else in the universe? Han (はん) Solo! If you watch Star Wars closely enough you can see him shooting geoducks with his blaster and catching them on fire for fun.
Currently there are no similar looking kanji which exist in the WaniKani learning system