This difference disappeared for the other visits on day 1 suggesting that the novelty of the situation was involved.
The first day of a session corresponded to a change in the diet of the cats.
One may have expected that the novelty of the diet should have caused more sniffing.
On the contrary the cats tended to sniff more LPK, a diet that they have already experienced,than VPK that they have previously experienced but without the addition of tuna.
The tuna was very odorant and it seemed that this odour was attractive enough to elicit eating in a short lapse of time