What is the difference between a thistle in the heather and a kiss in the dark The Ghost Goes West - 1935?

In the context of the film "The Ghost Goes West" from 1935, the phrase "a thistle in the heather" likely symbolizes something prickly or unpleasant, contrasting with the intimacy and warmth associated with "a kiss in the dark." This juxtaposition may represent the contrasting emotions or experiences portrayed in the movie, highlighting themes of love, mystery, and perhaps unexpected or conflicting situations. The use of these contrasting images could serve to create depth and complexity in the storytelling, engaging the audience on multiple levels.