I have a pretty basic question about interpreting the results from using the -contrast- command for interaction effects. In the example below, why does the interaction in the results from contrast give the same as in the regression, but the two effects on their own do not match the regression? (Using Stat 15)

Code:
sysuse auto, clear
tab for rep
drop if rep==1
drop if rep==2
reg mpg head trunk weight length i.for##i.rep
contrast i.for##i.rep, effect nowald