as linguists decipher elephant language, they are puzzled by what appears to be a large and recent body of loanwords from an unknown species, but eventually it is identified as 20th century truck engine sounds that have come to mean "[I am] moving towards [location implied]" furthermore there are multiple registers to it, with the 'train' register being more hissy and implying unstoppability, and the 'car' register (higher in pitch) indicating playfulness