Review the item:
Jenny noticed a greasy snail-like trail that snaked from the kitchen counter
onto the floor and then over to the hallway, June, Jenny's
cat,
had stolen another stick of butter and tried to drag it to the laundry
room.
Jenny's cat is an appositive. An appositive renames the noun that comes before it—in this case, June. An appositive will frequently interrupt the flow of a sentence, and when it does, as in the example above, you need to put a comma both in front and behind the interrupter.