Help to ynderstand please phrase from the film,,OVERBOAT''
1)wetherby you go.2) so were thumbs. 3)if not we get moths.

Question

Answer

You mean "Overboard"? :)

1) "Nice-looking Wetherby you got."

You got = you have. The next line tells us that it's a kind of gun.

2)  "Forks were invented so man could at least make a pretence of separating himself from the apes."  "So were thumbs."

We understand it as, "Also, thumbs were invented so man could..."

3) "One would think you would know closets are made of cedar. If not, we get moths."

If the closets are not made of cedar, we'll have a moth infestation.