That's a can of worms.

Meaning

That's a complex and potentially problematic situation.

Examples

• John: I think we should investigate this further.
• Alice: I'm not sure, John. It looks like <b>that's a can of worms</b> we don't want to open.
• John: But we need to know the truth.
• Alice: I understand, but we should carefully consider the consequences. This could be <b>that's a can of worms</b>.