So the last slime didn't taste great, but now Tom can't really taste anything (or see much, his eyes couldn't stay open for some reason) so it's really not a big deal. When a drop of goo lands in a small puddle in his path, and he looks up to see another round red eye staring down at him, he figures why not give it a little taste too? Maybe this one is better! Plus it's on the ceiling instead of the floor- surely that means it's a different breed or whatever.