Headcrab Problem

[Gooptek]

I am having a VERY hard time on learning how to cling to ceilings with Headcrab. Yes, I use him. But for fun, not for seriousness. His major gimmick is that he can cling to walls and ceilings. The "cling to walls" part was pretty easy to pull off, but the "cling to ceilings" part is what puzzled me. It didn't really seem that the character guide made by Steam user Kuhaa (which was pretty awesome BTW) could manage to explain it specifically for me. So, the thing is: How do I cling on to ceilings with Headcrab? I tried what it said on that guide, but I either did it wrong or I couldn't understand it correctly. Help is appreciated and will be rewarded with a "thank you".

[Kuhaa]

The reason it's unclear in my guide is that I managed to do it couple of times but then it suddenly stopped working. I didn't want to spend too much time on it so I just assumed it works the same than Ball of Goo. I decided to include it because someone pointed it out in comments, and from personal experience I know clinging to ceilings is possible with Headcrab. Unless it's a glitch. It would be nice if someone could clear this out so I can update the guide. :)