-I've got to confess unusual amount of persona bias today, even for Permanent Monday. I love spit takes. In physical/ photographic productions, spit takes are not only cheap, easy way to provide a striking visual image, and generate a surprising shock effect more interesting than a scream, but they externalize an emotional reaction in a semi-abstract manner only partially based on real behavior. You know what a spit take "means", even though people rarely, if ever, actually "do" spit takes.
-Garfield, toying with form, withholding spectatorial expectations, and conventional comics wisdom, eliminates the moment of release. The spit take itself falls between beats in the visual rhythms of the panels. The result is mildly deconstructive of comedy language, and a contribution to Garfield's running experimentation with denying the reader the moment of comic pleasure he is expecting, while supplying something he didn't know he wanted. Namely Jon covered in cat-spit and coffee.
-It is ambiguous if Garfield's spit take is motivated by skepticism that Jon is learning about women (uh, isn't he, probably? If anything, it's an honest admission that prior to having a steady, he didn't know anything about women), or he's amused by the unintentional (?) double-entendre Jon's made. I guess it's not really a double entendre, so much as the possibility he's talking about sexual knowledge. I don't see the point in being coy when talking about a comic strip about a cat spitting coffee on a nerd.