This paper explores the frequency of the usage of English words and expressions among primary school pupils during playing video games. It also examines the strategies in incidental EFL vocabulary learning. The research was conducted on a sample of 76 fourth and seventh grade primary school pupils learning English as a first foreign language. English words that are frequently used by pupils while playing video games have been gathered during informal conversations with pupils. A questionnaire survey was used in which participants’ understanding of the meaning of English words was tested. In addition, the use of strategies of incidental acquisition of English words and expressions was examined. It was assumed that there is a better understanding of the meanings of the words among seventh- grade pupils due to their longer exposure to formal and informal EFL learning. It was also assumed that seventh grade pupils have a better understanding of English words and expressions while using the strategy of acquiring unknown words from the context, also known as “the guessing strategy”. The research results have shown that pupils often use spontaneously acquired English words when playing video games. The findings of the study have also shown the differences in the understanding of the meaning of words among pupils depending on their exposure to the English language.