Always on the look out for something really weird, in 2006 I found this grotesque thing. The general impression is of a set of giant rotting teeth.
It didn't take much tracking down. Many fungi are host specific, so if you can tell what the fungus is growing on you stand a chance of identifying it. This rises to a good chance when the fungus is as distinctive as this. In this case the host was maize Zea mays and the fungus is maize smut Ustilago maydis. The fungus was growing on the cobs.
Though U. maydis is common in North America, it's very rare in the UK. This was only the ninth time that it had been recorded. It's unlikely to be overlooked, so it's probably genuinely rare. The field it was found in had Z. mays growing with other exotic grasses that had obviously been sown for game cover. As a result, I suspect that the field had not been sprayed with fungicides that would ordinarily prevent U. maydis from growing.
Apparently, in North America U. maydis has traditionally been, and is still considered by some, to be a good edible fungus. In fact I read that some cultures prize the fungus more than the sweetcorn. Would you eat this?