Yes, it’s a truffle but not one you would want to eat. This is a type of Slime truffle (Melanogaster genus – Latin for Black Stomach). A British truffle authority writing in 1844 said “A single specimen in a room is so strong as to make it scarcely habitable.” This one was found by primary schoolchildren in Oxford as part of their outdoor learning in a copse of beech trees in the school grounds.