The bottom rim of the fuel canister goes between those jaws, and acts as a lever to puncture the can. You use those canisters to fuel your camp stove, which you have because even if you’re cooking over an open fire your moka pot needs a stove. Some gas gets left behind even when it’s “empty”. As I understand it, it’s enough gas to cause problems at the recycling center. So instead the small hole allows it to bleed off into the atmosphere where it won’t explode. Pretty neat