Stranger still. The familiar can appear and disappear at Felix's will? Spock would have surmised it was some form of hologram or projection with that being the explanation but while it may look insubstantial it's quite solid. Very nearly alive, even.

"No, I suspect they will get quite a startle from that. Though I advise exercising caution in who finds out about such abilities."

The elder Vulcan doubts greatly that the younger captain will have even countenanced such an activity on his own. With Felix left in the dark about what the term even means, Spock considers the matter all but settled in Jim's unintentional favor. Unless Felix is the sort to kick up a fuss about what he's being denied however accidentally.

"It is not surprising that young Jim has failed to mention this to you. I'd venture a guess that it hasn't crossed his mind in the slightest."