They go to class

"Sorry we're late, sorry." Robyn announced as the two of them entered the room, it had been agreed that she would do the talking to keep the attention off Sandry.

"Nice of you to join us." The teacher said from near the back of the room, "take a book from my desk."

Sandry picked up a book, but it immediately slipped through her fingers.

"Whoops." She bent down to pick it up.

RIP!

The patch broke its stitches and the entire circle of material flew away from the trousers, unveiling the split seam and Sandry's underwear to the class.