Use of anus during sex; digital penetration of anus;
I found this in Diane Gabaldon's latest book "An Echo in the Bone", p. 121 and had no clue, although one could guess from the context. "He pulled out the finger and guddled her, light and quick, all along the slick deep parts..." in Jamie's effort to bring Clare to orgasm as quickly as possible. Here the word "guddled" is used to describe what was done after removing his finger from her anus, so messy would definitely apply. As always, the author finds wonderful ways to use Scottish slang words one has never heard of.
To insert one's finger(s) into a woman's vagina to pleasure her digitally, while simultaneously having penile-vaginal intercourse with her. (From the Scottish term used to describe the catching of a fish with one's hands by tickling it on its underbelly before snatching it out of the water.)
As used in Diana Gabaldon's novel, _An Echo in the Bone_: "He pulled out the finger (from her anus) and guddled her, light and quick, all along the slick deep parts, feeling his own cock under his fingers, big and slippery, stretching her..."