It's normal for kids or adults to "get really into" something. The difference between them and an autistic person who "gets really into" something is that the typical people will still do other things and in the case of children, the interest will likely pass by more quickly. With an autistic child the interest is MORE intense, MORE consuming, and lasts LONGER than with a typical child. Every interest Little Squirrel has had has been this way. Her friends will get interested in My Little Pony, and LS does too, but the friends will also have interests in Princesses, Spiderman, or other characters. But not LS. It was all MLP, all the time, for a very long time. That one was over a year. Before MLP was Angry Birds. All Angry Birds, all the time. After MLP was Phineas and Ferb. All P&F, all the time. Now it is Minecraft. This one will last longer, I can tell. Because she's not just obsessed with playing it but also with watching others play it on youtube (Stampy Cat and Amy Lee and Squid are the only ones she's allowed to watch). She doesn't watch or play anything else but Minecraft.
Interests quickly become obsessions and obsessions ever more quickly become perseverations. Watching Stampy Cat again and again is familiar and predictable. Playing Minecraft brings the comfort of being in a familiar world where she can control everything.
Even the squirrel perseveration started as a joke at school over a year ago, where she made a face that looked like a squirrel, then everyone laughed, so she did it again. And again. And again. That spiraled into this whole 'schtick' about squirrels that got the whole class involved (poor teacher). But what was just casual fun for her friends, to say SQUIRREL! and make squirrel faces, was all-consuming for LS. So now that it's over a year later and her friends have long ago moved on to new things, and LS is still doing the squirrel act, but not as much at school anymore since even the word alone has been outlawed in the classroom and her friends have long since been tired of it. So she saves it all up for home. For me. All squirrel, all the time.
Except for when she is doing the newer 'schtick' that involves a monkey face and scripted repetitive speech about a monkey. She alternates between the monkey and squirrel acts pretty equally. I don't prefer either one. They both make for a very long weekend. So people probably wonder why I let her play and watch Minecraft so much, I just can't even explain that at least she's quiet and it keeps the squirrel and monkey away.