  We lift the splicing formula of N\'emethi and Veys, which deals with
polynomials in two variables, to the motivic level. After defining the motivic
zeta function and the monodromic motivic zeta function with respect to a
differential form, we prove a splicing formula for them, which specializes to
this formula of N\'emethi and Veys. We also show that we cannot introduce a
monodromic motivic zeta functions in terms of a (splice) diagram since it does
not contain all the necessary information. In the last part we discuss the
generalized monodromy conjecture of N\'emethi and Veys. The statement also
holds for motivic zeta functions but it turns out that the analogous statement
for monodromic motivic zeta functions is not correct. We show some examples
illustrating this.
