When Liz is washing a horse, it has a lot of soap on its back. When the camera cuts back---from having cut to Richard observing her---almost all the soap has disappeared but no water was poured on the horse's back.
At the outdoors picnic, Liz gets up from the table. but Richard Keaton grabs her by the wrist, to prevent her from leaving. But when the close-up is shown, he is holding her by the fingertips.
It is never revealed why Mrs. Pram is, all of a sudden, hostile towards Liz, other than as a "red herring", to make the viewer believe she is the killer. After the real killer has been revealed at the end, all of a sudden again, she becomes all smiley and nice towards Liz. This made no logical sense.