If starting a new locaition, and only one rat is left, the "send rats" button is disabled, so you can't send the last rat.
E.g. Rat Shortage, send 400 rats works, but if you send 399 rats, drop the hook, go to the next location, you can't drop the hook with the last remaining rat.
Bug found repeatedly in the classroom yesterday:
If starting a new locaition, and only one rat is left, the "send rats" button is disabled, so you can't send the last rat.
E.g. Rat Shortage, send 400 rats works, but if you send 399 rats, drop the hook, go to the next location, you can't drop the hook with the last remaining rat.