Acid
Take some alcohol and put a spider in it to make acid. Spiders have a little acid in them already, but if you want something really potent, smash one up in some whiskey to make a deadly acid that'll rip through anything.
さん
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You're trying to find a container for this acid when Santa-san (さん) bursts through your wall. He frowns down at you. You're on the naughty list now. You killed spiders AND made dangerous acid? Ooooh you're in trouble.