Xiàqí de shíhou, tā zǒngshì níngshén sīkǎo, bàntiān yě bù shuō yí jù huà.
When he plays chess he thinks hard and can go a long time without saying a word.
Tips
usage
凝 is to congeal, so 凝神 pictures a scattered mind setting into one point. It is common in 屏息凝神 (to hold one's breath and concentrate), said of an audience watching something tense.