Scientific maxims are often used to describe common behaviours without any pretence of a common cause. The maxim ‘nature abhors a vacuum’ can be used to describe the distribution of molecules in a vessel or the migrations of birds. These maxims can often be replaced with other expressions (‘Brownian motion’, ‘flocking behaviour’) which can give better explanations when needed. In some cases, however, two seemingly disparate phenomena may have no better terms to account for them than those from natural language strategies. Perhaps this is because the phenomena in question are not as distant as they seem, or perhaps it is down to the fraught relationship between words and things. In the study of cooperation in biology, a great deal of research has been devoted to symbiotic relationships between plants and mycorrhizae fungi. The term used for how plants and fungi get together is ‘recognition.’ We would be inclined to say that this jargon is a pretty distant metaphor and should better rest on the more familiar biological maxim of ‘lock and key’ as analogy. I will forcefully argue that this inclination is wrong. I will also tentatively propose that the context of symbiosis has things to teach us about communication and metaphor, and maybe even ethics.