Dynamic tongue movements of intervocalic English and Japanese liquids are analysed based on ultrasound data obtained from 17 L1 Japanese and 12 L1 North American English speakers. Principal Component Analysis (PCA) identified three key articulatory properties, including variation in tongue retraction and height as well as tongue tip movement. The time-varying changes showed different magnitude and timing for tongue retraction for Japanese speakers compared to English speakers. Substitution of English liquids with Japanese /r/ was not clearly observed in the tongue movement pattern. The findings highlight the complexity involved in the articulation of English liquids in L2 speech and the usefulness of the finer-grained articulatory analysis in understanding the particular challenges L2 learners face in producing English liquids in L2 speech.