In a conversation with Toyota CEO Akio Toyoda, the exec confirmed that Tesla is in fact building two mule vehicles for the world's largest automaker -- specifically, "Tesla battery packs, power electronics and motors are being installed into Toyota bodies."

The statement was later confirmed by Tesla Chief Technology Officer J.B. Straubel to CNN Money.

The prototype vehicles are apparently for testing purposes only, to see if the Tesla power packs stand up to Toyota standards. It's an interesting mix, though, with the financially struggling start-up -- which did better than expected during its recent initial public stock offering -- that sees itself as more of a Google-type company than, say, a Ford, working with the world's largest automaker.