Building factors across two columns, is this possible?

I am trying to make it so two columns with similar data use the same internal numbers for same factors, here is the example:

read.csv("test.csv",header =FALSE,sep=",")

V1    V2       V3
1   sun  moon    stars
2 stars  moon      sun
3   cat   dog   catdog
4   dog  moon      sun
5  bird plane superman
6  1000   dog     2000

data <- read.csv("test.csv",header =FALSE,sep=",")
str(data)

'data.frame':	6 obs. of  3 variables:
 $ V1: Factor w/ 6 levels "1000","bird",..: 6 5 3 4 2 1
 $ V2: Factor w/ 3 levels "dog","moon","plane": 2 2 1 2 3 1
 $ V3: Factor w/ 5 levels "2000","catdog",..: 3 4 2 4 5 1

as.numeric(data$V1)

[1] 6 5 3 4 2 1

as.numeric(data$V2)

[1] 2 2 1 2 3 1

as.factor(data$V1)

[1] sun   stars cat   dog   bird  1000 
Levels: 1000 bird cat dog stars sun

as.factor(data$V2)

[1] moon  moon  dog   moon  plane dog  
Levels: dog moon plane


So notice "dog" is 4 in V1, yet its 1 in V2.  Is there a way, either on import, or after, to have factors computed for both columns and assigned
the same internal values?

Brian