Fridge Brilliance: Though used to set up the Chekhov's Skill for Tank, the tortoise's plan of tipping over Opal's cage on top of her from behind would have been rather effective to get the mouse from her if the butterfly hadn't beaten him to it. In general, Tank appeared to have several moments of genius hampered by being a slow tortoise than anything else.
Of course Rainbow Dash would keep the pet that stopped to help her. Which Element of Harmony does she bear? Loyalty.
When Applejack points out that there's been an avalanche in the valley, for a moment just before Pinkie and Fluttershy spot Tank with Rainbow Dash in tow they have no idea what happened. For all they know, Rainbow Dash could've been crushed under the rocks. In this light, Applejack's fear and urgency take on a much darker tone. It's even worse if you consider that, from this perspective, that she may not have been immediately killed, but badly broken, suffering great pain as she slowly suffocates.
Rainbow Dash mentioned near the end of the episode that Tank is, "like a tank." This is all fine and well until you ask yourself, "How does Rainbow Dash know about the existence of mechanized warfare?"