In the conventional Stirling engine, a fixed amount of helium is compressed in a cool chamber and then transferred to a chamber heated by an external burner.

CNN: Lab develops engine for the future

One recent weapon is what frog-busters are calling a "hot shower chamber, " a modified freight container used by nurseries to ship plants, with multiple heads that spray heated water onto the plants and kill any coquis that might be lurking there.

WSJ: When It Gets Too Noisy in Paradise, They Call the Frog Whisperer