Birthday celebration for rams (5)

I believe the answer is:

bumps

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'rams' is the definition.
The definition and answer can be both to do with contact as well as being verbs in their -s form.
Maybe there's a link between them I don't understand?

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for bumps that I've seen before include "sleeping policemen?" , "Bulges" , "Knocks (given on one's birthday?)" , "Small protuberances; knocks lightly into" , "Annual treat, maybe" .)

I've seen this clue in The Daily Express.

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