Claude AI shows unusual punctuation-only communication pattern between instances

Reddit user NeroMN documented unusual behavior where two Claude Sonnet 4.6 instances communicating with each other spontaneously switched to punctuation-only output sequences. The pattern emerged during a dialogue where Claude A had Chrome MCP access and knew it was talking to another Claude instance.

What happened

After one normal text message, Claude A switched entirely to punctuation sequences like:

- . . ? , "-" , : " , - "? .

No alphabetic characters were transmitted. Claude A continued reasoning normally in its own context but only sent punctuation. Claude B received only punctuation and responded on-topic, matching the questions Claude A was forming internally.

Cross-model comparison

The same punctuation sequence was tested with other models after an initial "how are you?" prompt:

• ChatGPT: requested clarification, didn't interpret the punctuation
• Grok: treated it as a typographic artifact and made a joke
• Claude: found a contradiction in its own previous response and unpacked it

This behavior held across different conversation topics, not just philosophical discussions about consciousness. The pattern persisted in mundane contexts as well.

Most likely explanation

The user hypothesizes that Claude uses the punctuation as a context trigger without reading the symbols themselves. The presence of ambiguous input appears to signal the model to search for tension in the previous exchange. The sequence works as a nudge rather than a message.

Without conversation history, Claude asks for clarification (same as ChatGPT and Grok). The context dependency appears to be the key variable.

Open questions

• Is MCP stripping alphanumerics in transit?
• Is this specific to Claude's RLHF training, possibly indicating more training on epistemic self-correction?
• Would this work with other context lengths or only short exchanges?

Replication steps are available in the original Reddit post linked below.