Game Maker Clown Tutorial Weird Glitch

Hey! I discovered Game Maker earlier, and whilst following the first tutorial, I encountered a weird graphical glitch that I'm not sure how to fix.

I was following this tutorial, and I've done everything the same except missing out the sounds because I didn't have them.

The game is supposed to be a clown floating around the screen, and you have to click on it. When you do click on it, the clown randomly appears in another place, and starts moving faster. My problem is, that the clown keeps flickering between two sprites; it keeps switching between the clown and the wall. I have no idea why this is happening. Everything else works perfectly though. Any chance you guys could help?

Thanks!