#300: Stephen Quant of https://catbehaviorhelp.com/ often gets consulted about a cat peeing on vertical surfaces, usually by backing up to the area in question. Often with a high and quivering tail. The cat will then shoot a stream of urine on the vertical surface. Stephen explains that this is not intended as urination, but is actually spraying as a territorial marker, so he explains ways to reduce the cat's need to do that.