> Maybe it is that thawing happens in reverse with the extremities, then the rest of the system thawing, with the heart being last

FTA: In spring, the wood frog thaws from the inside outward. First the heart starts beating. Then the brain activates. Finally, the legs move.

The article says that, but it can’t be the normal meaning of thaw. Thermodynamically, onbiously the innermost portion of the volume is going to warm last. But in terms of the frog’s system restart order, that order makes sense.

The inside of the frog isn't actually frozen, because it's glucose-flushed.

So the sequence is more:

   1. Outside of frog thaws
   2. ??
   3. Heart starts beating

This frog is alive. It could detect that long-term thaw is imminent (say from sensors on its skin) and start some processes that produce heat around its heart.