front of bertha in hopes of sending workers to the front of the drill to see what she's up against. >> you can't back up. >> reporter: bertha won't be moving forward until at least early next year, after the mystery is solved. stephanie elam, cnn, los angeles. >> how did that conversation go? i've designed a five-story tall, completely dominant digging machine but it doesn't go in reverse. >> i'm sorry. it isn't funny. it's going to be expensive to figure it out but it is funny. >> they just assume wherever they pointed this thing, it would always go. >> when it's that big. >> i was trying to think of something creative. it can't just be a big rock. that has to be the very basic nature of what big bertha could do is break down rock. >> what do you think it is? >> no know. you guess. >> i have nothing. if i knew i wouldn't be asking