When Susan is taking a bath, her breasts are covered with a smiling face of a cartoon cat. It has to be seen to be believed. Doubles as Hypocritical Humor, because by this point we've already been treated to a lot of exceedingly violent, gruesome and depressing scenes, the sight of Susan taking her pants down, sitting down on the toilet and peeing and actual female frontal nudity (though the nude female in question is a corpse; maybe the UK, where this game was made, has different rules concerning nude cadavers).
Choosing the Giant Zombie Cat option while telling the legend of the Cat Widow.
The entire event where you can call the police for help when kidnapped by the second and third parasites. Good grief, Police Are Useless indeed.
Susan describing her kidnappers contains a funny line from her:
Susan:He's got a wife...she poured bleach down my face...Bitch...*said in a tone as if she poured bleach on her clothes and not on her face*
Rita, the thick babysitter and Susan's irritated conversation with her.
The conversation with the old man in Flat 5 due to his odd behaviour possibly brought down by early stages of dementia. This line is a humorous example, as he is convinced that Susan and Mitzi are caretakers who are trying to get him out of the house:
Old Man:I can manage, I've done it all my life and it'll stay this way. I can still cook my bed and I make my dinner every morning all by myself!
Then this moment becomes a "Funny Aneurysm" Moment, as the Old Man is actually faking his dementia and is trying to ward suspision not from himself, but from his paralysed son, who is The Eye of Adam.