To establish the relationship between a facilitative contextual factor and reading ability, the present study investigated the comprehension of humorous "parental brain twisters" in cross-cultural ESL situations as related to English proficiency. Japanese ESL students were able to translate the sentences of parental brain twisters from English to Japanese, but this does not mean they actually understood their contexts. While there was no significant difference in translating English among the three ESL student groups, which were divided by their English proficiency, a significant difference was found in the students' understanding of their humorous contexts. Since all lexical items in the sentences were equally well understood by all three groups, students with better English proficiency were more sensitive to context. This result further suggests that a higher level of English proficiency includes understanding of social and cultural context, as well as a knowledge of English.