A lot of people are having issues with Basil. Well...A few. But enough people that I think I should give a thorough guide on how to complete the h-scene with the adorable little lizard. Now part of the fun is figuring it out on your own, at least in my opinion. But if you can't figure it out, look below. However, if you don't want to be spoiled on how to complete it, do not look below!
Start with scratching his head and ear flap things. You should get a lot of red hearts by doing this. Basil will start to go through various stages of erection. It goes in-sheath, poking out of sheath, completely out of sheath, full-mast. But you are gonna have to wait until his dick is completely out of his sheath to continue to the next step.
Now the tricky part. You have to stroke his dick (tip: hold down left click and drag it up and down 3 time) followed by sticking your fingers in his mouth (tip: hold down left click and drag it up and down like with stroking his dick, but continue until red hearts appear). Repeat this until Basil hits full mast.
Now, you are technically done. You can continue like that if you want, you don't stop getting red hearts. However, upon reaching full mast, you can add sticking your fingers into his ass. So it becomes ass, dick, mouth (tip: hold down left click and drag it up and down 3 times for the ass, the other two are until hearts appear).