LOL What a priceless picture of pony paranoia, Tickles me good, hoo hoo!
All I can say is her expression and body posture says it all perfectly, as if she had been walking carefreely up to it when it started laughing and then she was so brindled by it that she starts taking a step back.
Another Awesome Job Buddy, You're a talented artist to be sure! And more importantly than me saying it is the fact for you to believe it before anyone says anything.
Take care and You'll do many a wonderful thing when you use your talents to glorify God who gave you these talents!
Really good work! Is is very hilarious! Her tail looks hipnotic indeed (Rarity is drawn very well) and also the background is well done! I especially like the sand - it looks very realistic regardless it's simplicity.