On the other side of the doorway from 'Witcher George' is another painting with serpents. Geralt says "Witchers are better with a sword than a paintbrush" when he approaches it. This painting features a man in a pose identical to the sculpture of Laocoön and His Sons, battling with snakes.
PFI reference from one of the guards near the gates of Old Vizima in Chapter II, and "Poor Fucking Infantry" graffiti on recruiting poster in Temple quarter. British acronym from WW1 and WW2. (There is also a reference to the Poor Fucking Infantry in the Witcher saga books, at least in Polish and Czech version. In-game PFI might rather be a reference to the Witcher saga.)
In several houses player can see a portrait of a man clad in red clothes and holding a golden mace. The portrayed man has a face of Maciej Miąsik, Chief Production Manager of The Witcher. The painting itself is a copy of Brodero Matthisen's portrait of Stefan Czarniecki.
Note: Most of these are random events — when walk by a townsperson, he/she may utter something that will make you laugh. Their randomness makes it quite possible to miss them, though.
If you listen closely to the music during the cut scene in Chapter II where the boat is moving away from the docks (from Vizima to the Swamp) and the camera focus moves to the surface of the water, you can hear a musical cue similar to the Jaws theme.
Sometimes you hear people muttering the phrase "Plans within plans within other plans."; which is a quote from the Dune novel by Frank Herbert.
In the Druids' grove, one of the druids asks "Are you a fool seeking a magical strength-giving beverage?", which is an allusion to the Asterix-comic books.
(Only in Polish language version) During the party in the Shani's house during Old Friend of Mine after you are told to go downstairs, Dandelion sings: "Wypijmy za Błędy" (English: "Let's drink to our mistakes") and later: "Za błędy na górze", which are parts of the Ryszard Rynkowski's song titled "Wypijmy za błędy".
The bookseller in Trade Quarter (To access him, you need to reach ACT III) sells a book about Dagon.
The person who invented explosives in The Witcher is called Alfred Nabel, and it is stated in the Prologue by Eskel that he did not intend his invention to be used to blow things up. This is a reference to Swedish innovator Alfred Nobel, who invented dynamite and later on deeply regretted his inventing of the explosive due to its use on the battlefield as a means of killing. This led him to use the great fortune dynamite brought him to fund the Nobel Prize.
Monty Python references:
There is a discussion between lumberjacks about wild flowers and cross-dressing.
Poor people in the Temple Quarter slums will sometimes say "Society made me what I am!" as Geralt passes by.
(?) Three towers in the swamp. In Monty Python and the Holy Grail there is a scene where Micheal Palin's character talks about building four castles in the swamp, three of which sank, burned or both — reminiscent of the mage.
There is a character named Patrick De Weyze in Chapter III — reference to Patrick Swayze or just a name in dutch (Patrick De Weyze would translate into Patrick The Wise)
Chapter IV, when talking to the healer about Alina's mirror, Geralt quotes, "Who is the fairest of them all?", quote made famous in Snow White and the Seven Dwarves, when the evil queen asks her mirror that question, it replies that she is very beautiful, but that there is one more beautiful still, Snow White.
When the Lady of the Lake gives Geralt the silver sword Aerondight (Chapter IV), she is knighting Geralt — the phrases she uses are clearly taken out of the Kingdom of Heaven movie (the scene where the Baron of Ibelin passes his title to his son Balian, right before he dies).
Ramsmeat says the same thing to you when you piss him off as Jules does in Quentin Tarantino's Pulp Fiction:
Ramsmeat: Do I look like a whore?
Geralt: yes or no
Ramsmeat: Then why you trying to fuck me like one?
Jules: What does Marsellus Wallace look like?
Brad: He's bald, he's black...
Jules: Does he look like a bitch?
Jules: Then why you trying to fuck him like one?
Bootblack who you meet in front of the detective's house is as well informed about the city as the character "Johnny" in the Series Police Squad.
Kalkstein lives in the "ghetto" and is Jewish both in his name, his accent and his Sephardi resemblance. Possibly a reference to Einstein (who was Ashkenazim) or other Jewish scientists. Kalkstein also means "limestone" in German and Norwegian, which was once used in chemistry to neutralize acid substances.
Possible X-Files reference: During the Long Way from Home quest, Geralt, (who comes across as an atheist), asks Vaska about gifts to the water lords, but Vaska refuses, since he is not a believer. Geralt states emphatically "I wish to believe!", then Vaska tells him. Possible reference, or miss-translation of X-Files, "I want to believe".
While having a conversation with Thaler during Posh Reception quest, Thaler mentions that the enemies who seek to destroy Temeria were going to, among other things, "steal our women". Geralt's response might be a reference to Duke Nukem as he says: "Who's this enemy? Who tries to steal our women?"
Chapter III, the alchemist in the workshop mentions that he is working on "the riddle of steel", a reference to the 1982 film Conan the Barbarian.
In the Epilogue the dialogue between the Kings Foltest and Radovid is almost a direct quote from Times of Contempt, which itself is a clear reference to Warsaw Pact invasion of Czechoslovakia in 1968 (Soviets claimed they came to provide "fraternal assistance" to the Czechoslovak people.)
Foltest: Radovid, your armies must subdue the Order in Redania and in the north of my lands.
Radovid: My armies will embark on a mission of fraternal assistance.
Foltest: I don't want any fucking fraternal assistance.
Some NPCs mention "law and justice" which is a reference to the controversial Polish then incumbent ruling party — Law and Justice.
Kalkstein is President of Poland's "real surname", according to "the list of Jews", and his gnome-roots, mentioned in the journal, are references to the small size of Kaczyński twins and the fact, that they are often called gnomes.
Ramsmeat — Polish "Baranina" (lit. Mutton) — was a nickname for a Polish Mafia boss.
Other ads may have some relation to Polish culture.
Adam, the villager from Chapter IV is a reference to another polish Romantic poet, Adam Mickiewicz. Celina's remark that Adam behaves "as if he was suffering for millions" is a quote from Mickiewicz's poem.
The poem Dandelion and Geralt recite when breaking the spell holding Alina the Noonwraith is the beginning of the poem Upiór (The Wraith, also translated as The Ghost). Dandelion later remarks that he intends to elaborate this poem further and turn it into drama about folk rituals. The Wraith is a part of a drama The Forefathers that deals, among others, with folk rituals.
When Geralt comes to Alina after he learns about the mirror, Alina begins her greeting with two seemingly unrelated sentences. These are quotations from the song W południe (At Noon) also known as Południca (The Noonwraith) by Kazimierz Grześkowiak.
After Geralt criticizes Dandelion for Woolseying the events he is supposed to commemorate, Dandelion remarks that "there is a truth of the moment and the truth of the legend". This is a direct reference to the movie Miś by Stanisław Bareja.
The recruiting poster for the Order of a Flaming Rose is based on famous Lord Kitchener Wants You poster from 1914.
The inscriptions on the the signs and some posters use glagolitsa, although most inscriptions comprise of random letters. Some signs have the phrase 'Narakort' [like the one above City Dungeon] or 'na sprzedasz' (garbled for sale in Polish) [the ones at the gates of Vizima cemetery or Lebioda's hospital].