I have two pet rats, and I’m pretty confident that they’d love a trebuchet. I could see one of them operating while the other is the ammunition.
Or, both operating with more conventional projectiles. Rats crave destruction and chaos. And also cuddles.
I know someone with obsessive compulsive disorder, and I could see a chatbot being harmful there, depending on how it goes. A lot of compulsions are around checking or asking for reassurance. A chatbot would provide endless reassurance where a human might eventually get annoyed and cut you off. It would allow you to ruminate endlessly.
The problem is that engaging in compulsions keeps you in a cycle - it’s never enough reassurance. The gold standard treatment is exposure response prevention (ERP), where you intentionally expose yourself to triggers and resist doing the compulsions. (Info from Free Yourself from OCD by Jonah Lakin, PsyD)