Fingers on his mouth when he kisses her?

Did anyone else notice, in the love scene between Matthew Settle and Gretchen Mol that (after the phone rings) he goes to kiss Mol (who is under him) and he puts his fingers over his mouth? Like he's trying to cover his lips so they don't touch hers? Strange. What is that about?

"...nothing is left of me, each time I see her..." - Catullus