After Walter Slezak walks behind Rock Hudson into the mansion foyer, he says to Hudson "I'll take your rooms to your bag," after which one can notice the peculiar reaction of Hudson.
Boom mic pole casts a shadow across the characters and house when the boys arrive at the villa, and Rock Hudson is running them off. It pulls away right after Bobby Darin asks if it is legal for their reservations to be denied.
Early in the film, the Jeep driven by the 4 young American guys goes off an embankment and lands in the waters of a lake or river, with the Jeep being nearly submerged in muddied waters. The Jeep, their clothing and attached luggage, are obviously waterlogged. And yet, the next day, the 4 guys show up at Robert Talbot's villa in this same Jeep - now clean as a whistle, with their clothing as well as their luggage all in pristine condition.