If Signal is 0, then only a check for existence of the process is performed. In this case, kill/2 fails if the process does not exist.
Success: [eclipse]: get_flag(pid, Pid), kill(Pid, 31). Signal 31 Pid = 2929 yes. [eclipse]: kill(2929, 0) yes. Failure: [eclipse]: kill(9999, 0) no.