I got all the BATS, including the hidden theme word.

Then my first slip was to assume from the “definitions” that TUN was sufficient for the theme word NUTS. I thought of grapenuts but could not find it in Chambers, so opted for COKERNUTS, PALMYRA NUTS and CREAM NUTS (aka Brazil Nuts).

This left me with FIRE and GRAPE and I eventually came up with WILD FIRE, WILD GRAPE and, from the bottom left corner of the grid, going north-east, WILD CATS. So my word below the grid was WILD, which also indicates instability.

Not as neat as the intended solution but a plausible alternative, I would suggest. Perhaps my mistake was to tackle it on April Fool’s Day!

I was surprised that there was only one response for this puzzle. Presumably a lot of solvers completed the grid and then came to a halt.

We enjoyed the puzzle – we think our experience was much like yours. Quite a few unusual words along the way but all fair but that’s what we expect with Phi so thanks to him as well!