Answer: Having a feeling of uneasiness or embarrassment.
Step-by-step explanation:
Journey to the Center of the Earth (1864) is a science fiction novel by Jules Verne. It is a story about a German professor, convinced that volcanic tubes are going towards the center of the earth.
In this particular excerpt, Harry is describing his uncle, professor Hardwigg. According to him, Hardwigg is a rather educated man, but it is sometimes very hard to understand what he is trying to say. Professor would often include complex adjectives or hardly pronounceable names in his speech, which would make him stammer. This would cause him to feel embarrassed, so he would give up speaking and have a glass of water.