In bombardier beetles these secretions are mixed with volatile compounds and ejected by a small combustion with a loud popping sound and a cloud of hot and acrid gas. This can injure small mammals, such as shrews, and may kill invertebrate predators outright. To humans, getting "bombed" by a bombardier beetle is a decidedly unpleasant experience. This ability has evolved twice – in the flanged bombardier beetles (Paussinae) which are among the most ancient ground beetles, as well as in the typical bombardier beetles (Brachininae) which are part of a later lineage. 