"Care to elaborate?"

• ''In what way?''
• "Why do you think that?"
• "In what possible way?"
• "Can you explain?"
• "Can you explain that further?"
• "Explain ..."
• "Why?"
• In what way?

Wiktionary Word definitions in Wiktionary
adv. 1 however#Conjunction, in whatever manner. 2 However, to whatever extent.