The TARDIS completely disregards the approaching stray cat, being quite used to the more intrepid of the local wildlife using her as perches or sometimes a source of warmth. She wouldn't even deign the animal with attention when it meows at her, except that's when she picks up the tiny life sign that is Andrew. A very small Andrew riding a cat. She definitely wasn't expecting that.

But thankfully the Doctor is home, so she won't have to deal with this confusing turn of events herself. Quickly getting over her initial bafflement, she opens the door to bring Andrew to safety and then gives the Doctor a rather alarmed mental nudge to draw his attention away from the recalibrations he's been doing. She throws in a few rapidly blinking lights on the console for good measure, just to express how startling she finds this.